DROP relation IF EXISTS Docs and Tests - Bug Fix

diff --git a/doc/src/sgml/glossary.sgml b/doc/src/sgml/glossary.sgml
index 25b03f3b37..c517ff5b4a 100644
--- a/doc/src/sgml/glossary.sgml
+++ b/doc/src/sgml/glossary.sgml
@@ -1612,6 +1612,30 @@
    </glossdef>
   </glossentry>
 
+  <glossentry id="glossary-type">
+   <glossterm>Type</glossterm>
+   <glossdef>
+    <para>
+     All data stored within the database is typed.  Each type has both a name, and associated
+     properties, as well as an overarching Type, of which there are two variations. Extensible
+     types can created by users and comprise of: base, composite, domain, enum, and range. There
+     are also the system-only pseudo-types.  Type records are stored in pg_type and the
+     overarching type is found in pg_type.typtype.
+    </para>
+   </glossdef>
+  </glossentry>  
+
+  <glossentry id="glossary-type-definition">
+   <glossterm>Type Definition</glossterm>
+   <glossdef>
+    <para>
+     Collective term for the various <glossterm linkend="glossary-type">Type</glossterm>
+     variants that are allowed for pg_type.typtype catalog table column values;
+     specifically, ones that are extensible.
+    </para>
+   </glossdef>
+  </glossentry>
+
   <glossentry id="glossary-unique-constraint">
    <glossterm>Unique constraint</glossterm>
    <glossdef>
diff --git a/doc/src/sgml/ref/drop_domain.sgml b/doc/src/sgml/ref/drop_domain.sgml
index b18faf3917..8b04b3818b 100644
--- a/doc/src/sgml/ref/drop_domain.sgml
+++ b/doc/src/sgml/ref/drop_domain.sgml
@@ -30,7 +30,9 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
 
   <para>
    <command>DROP DOMAIN</command> removes a domain.  Only the owner of
-   a domain can remove it.
+   a domain can remove it.  The duplicates the functionality provided by 
+   <xref linkend="sql-droptype"/> but restricts the object type to domain.
+
   </para>
  </refsect1>
 
@@ -42,8 +44,13 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the domain does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any 
+      <glossterm linkend="glossary-type-definition">type definition</glossterm>
+      with the provided name.
+      If no type definitions are found a notice is issued and the command ends.
+      If a type definition is found then one of two things will happen:
+      if the type definition is a domain it is dropped, otherwise the command fails.      
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_foreign_table.sgml b/doc/src/sgml/ref/drop_foreign_table.sgml
index 07b3fd4251..0288fb2062 100644
--- a/doc/src/sgml/ref/drop_foreign_table.sgml
+++ b/doc/src/sgml/ref/drop_foreign_table.sgml
@@ -42,8 +42,11 @@ DROP FOREIGN TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceabl
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the foreign table does not exist.
-      A notice is issued in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a foreign table it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_index.sgml b/doc/src/sgml/ref/drop_index.sgml
index 0aedd71bd6..dff437cf9b 100644
--- a/doc/src/sgml/ref/drop_index.sgml
+++ b/doc/src/sgml/ref/drop_index.sgml
@@ -70,8 +70,11 @@ DROP INDEX [ CONCURRENTLY ] [ IF EXISTS ] <replaceable class="parameter">name</r
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the index does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is an index it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_materialized_view.sgml b/doc/src/sgml/ref/drop_materialized_view.sgml
index c8f3bc5b0d..6647a0db0d 100644
--- a/doc/src/sgml/ref/drop_materialized_view.sgml
+++ b/doc/src/sgml/ref/drop_materialized_view.sgml
@@ -43,8 +43,11 @@ DROP MATERIALIZED VIEW [ IF EXISTS ] <replaceable class="parameter">name</replac
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the materialized view does not exist. A notice
-      is issued in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a materialized view it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_sequence.sgml b/doc/src/sgml/ref/drop_sequence.sgml
index 387c98edbc..b3209d6d01 100644
--- a/doc/src/sgml/ref/drop_sequence.sgml
+++ b/doc/src/sgml/ref/drop_sequence.sgml
@@ -42,8 +42,11 @@ DROP SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [,
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the sequence does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a sequence it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_table.sgml b/doc/src/sgml/ref/drop_table.sgml
index bf8996d198..9c9147f2ef 100644
--- a/doc/src/sgml/ref/drop_table.sgml
+++ b/doc/src/sgml/ref/drop_table.sgml
@@ -55,8 +55,11 @@ DROP TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ..
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the table does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a table it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_type.sgml b/doc/src/sgml/ref/drop_type.sgml
index 9e555c0624..305a62486f 100644
--- a/doc/src/sgml/ref/drop_type.sgml
+++ b/doc/src/sgml/ref/drop_type.sgml
@@ -42,8 +42,17 @@ DROP TYPE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the type does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any 
+      <glossterm linkend="glossary-type-definition">type definition</glossterm>
+      with the provided name.
+      If no type definitions are found a notice is issued and the command ends.
+      If a type definition is found then it will be dropped. This includes
+      domains even though they have their own drop command.
+      
+      However, an attempt to drop the automatically created composite type of an
+      existing relation will fail as the relation has a dependency on the found
+      type definition.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_view.sgml b/doc/src/sgml/ref/drop_view.sgml
index a1c550ec3e..ff75410cf1 100644
--- a/doc/src/sgml/ref/drop_view.sgml
+++ b/doc/src/sgml/ref/drop_view.sgml
@@ -42,8 +42,11 @@ DROP VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the view does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a view it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/test/regress/expected/drop_if_exists.out b/src/test/regress/expected/drop_if_exists.out
index 5e44c2c3ce..b57ddc2e60 100644
--- a/src/test/regress/expected/drop_if_exists.out
+++ b/src/test/regress/expected/drop_if_exists.out
@@ -330,6 +330,167 @@ HINT:  Specify the argument list to select the routine unambiguously.
 -- cleanup
 DROP PROCEDURE test_ambiguous_procname(int);
 DROP PROCEDURE test_ambiguous_procname(text);
+-- Demonstrate namespace collision behavior
+CREATE SCHEMA test_if_exists_first;
+CREATE SCHEMA test_if_exists_second;
+SET search_path TO test_if_exists_first, test_if_exists_second;
+DROP TABLE test_if_exists_second.test_rel_exists;
+ERROR:  table "test_rel_exists" does not exist
+DROP TABLE IF EXISTS test_if_exists_second.test_rel_exists;
+NOTICE:  table "test_rel_exists" does not exist, skipping
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TABLE test_if_exists_first.test_rel_with_index (ai int, bi text);
+-- table presence in the second schema causes a failure here
+-- even though a corresponding non-schema-qualified create
+-- statement would succeed.
+DROP VIEW IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a view
+HINT:  Use DROP TABLE to remove a table.
+DROP INDEX IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not an index
+HINT:  Use DROP TABLE to remove a table.
+DROP TYPE IF EXISTS test_rel_exists;
+ERROR:  cannot drop type test_rel_exists because table test_rel_exists requires it
+HINT:  You can drop table test_rel_exists instead.
+DROP SEQUENCE IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a sequence
+HINT:  Use DROP TABLE to remove a table.
+DROP MATERIALIZED VIEW IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a materialized view
+HINT:  Use DROP TABLE to remove a table.
+DROP FOREIGN TABLE IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a foreign table
+HINT:  Use DROP TABLE to remove a table.
+-- a role is not a relation so this shouldn't be affected
+DROP ROLE IF EXISTS test_rel_exists;
+NOTICE:  role "test_rel_exists" does not exist, skipping
+--      type affirmation (this isn't the same as the implicit type created with the table)
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c text, d int);
+--      existence of type prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP TYPE to remove a type.
+--      cleanup
+DROP TYPE IF EXISTS test_rel_exists;
+--      view affirmation
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+--      existence of view prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP VIEW to remove a view.
+--      cleanup
+DROP VIEW test_rel_exists;
+--      index affirmation
+CREATE INDEX test_rel_exists ON test_if_exists_first.test_rel_with_index (ai);
+--      existence of index prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP INDEX to remove an index.
+--      cleanup
+DROP INDEX test_rel_exists;
+--      sequence affirmation
+CREATE SEQUENCE test_rel_exists;
+--      existence of sequence prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP SEQUENCE to remove a sequence.
+--      cleanup
+DROP SEQUENCE test_rel_exists;
+--      materialized affirmation
+CREATE MATERIALIZED VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+--      existence of materialized view prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP MATERIALIZED VIEW to remove a materialized view.
+--      schema qualification works though (and cleanup)
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP MATERIALIZED VIEW test_rel_exists;
+DROP TABLE test_if_exists_first.test_rel_with_index;
+-- Type & Domain behavior is thus:
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      domain dropping errors with presence of table; no hint provided
+DROP DOMAIN IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+--      domain affirmation
+CREATE DOMAIN test_rel_exists int4;
+--      existence of domain in first search_path schema
+--      does not prevent second search_path table dropping
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP DOMAIN test_rel_exists;
+--      setup
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      type with same name exists as table creation creates a composite type
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+ERROR:  type "test_rel_exists" already exists
+--      domain creation with same name as table fails as auto-generated type conflicts
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+ERROR:  type "test_rel_exists" already exists
+--      cannot independently drop a composite type associated with a table
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  cannot drop type test_rel_exists because table test_rel_exists requires it
+HINT:  You can drop table test_rel_exists instead.
+--      cleanup
+DROP TABLE test_if_exists_second.test_rel_exists;
+--      setup
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+--      auto-created type (which is added also as a relation) prevents table from being created
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+ERROR:  relation "test_rel_exists" already exists
+--      a composite type is not a domain so a conditional drop fails
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  "test_if_exists_second.test_rel_exists" is not a domain
+--      can still create a domain in the first schema
+CREATE DOMAIN test_rel_exists int4;
+--      unlike the case with relations the fact that domains
+--      and other extensible types share the same namespace
+--      doesn't cause a DROP TYPE command that first
+--      finds a domain to fail - though it does prevent
+--      the search algorithm from looking in the second
+--      schema for an exact match.
+DROP TYPE IF EXISTS test_rel_exists; -- This removes the domain
+ --     type present, not a domain
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  "test_if_exists_second.test_rel_exists" is not a domain
+--      Yep, domain seems to have been removed
+DROP TYPE IF EXISTS test_if_exists_first.test_rel_exists;
+NOTICE:  type "test_if_exists_first.test_rel_exists" does not exist, skipping
+--      Yep, domain removed, finding the type
+DROP DOMAIN test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+--      cleanup
+DROP TYPE test_rel_exists;
+--      test with domain second and type first
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c int, d text);
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+--      fails since the first matched name is not a domain
+DROP DOMAIN IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+--      remove the matching type
+DROP TYPE IF EXISTS test_rel_exists;
+--      drop type cleans up domains...
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists; 
+--      ...so it no longer exists here
+DROP DOMAIN IF EXISTS test_rel_exists;
+NOTICE:  type "test_rel_exists" does not exist, skipping
+-- /Type & Domain
+-- Bug # 16492 - this script produces an error, arguably it should not
+CREATE TABLE test_if_exists_first.test_rel_exists (a int, b text);
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+NOTICE:  view "test_rel_exists" does not exist, skipping
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP VIEW to remove a view.
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP VIEW test_if_exists_first.test_rel_exists;
+-- /Bug # 16492
 -- This test checks both the functionality of 'if exists' and the syntax
 -- of the drop database command.
 drop database test_database_exists (force);
diff --git a/src/test/regress/sql/drop_if_exists.sql b/src/test/regress/sql/drop_if_exists.sql
index ac6168b91f..5cb7f17875 100644
--- a/src/test/regress/sql/drop_if_exists.sql
+++ b/src/test/regress/sql/drop_if_exists.sql
@@ -296,6 +296,142 @@ DROP ROUTINE IF EXISTS test_ambiguous_procname;
 DROP PROCEDURE test_ambiguous_procname(int);
 DROP PROCEDURE test_ambiguous_procname(text);
 
+-- Demonstrate namespace collision behavior
+CREATE SCHEMA test_if_exists_first;
+CREATE SCHEMA test_if_exists_second;
+SET search_path TO test_if_exists_first, test_if_exists_second;
+
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP TABLE IF EXISTS test_if_exists_second.test_rel_exists;
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TABLE test_if_exists_first.test_rel_with_index (ai int, bi text);
+
+-- table presence in the second schema causes a failure here
+-- even though a corresponding non-schema-qualified create
+-- statement would succeed.
+DROP VIEW IF EXISTS test_rel_exists;
+DROP INDEX IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_rel_exists;
+DROP SEQUENCE IF EXISTS test_rel_exists;
+DROP MATERIALIZED VIEW IF EXISTS test_rel_exists;
+DROP FOREIGN TABLE IF EXISTS test_rel_exists;
+
+-- a role is not a relation so this shouldn't be affected
+DROP ROLE IF EXISTS test_rel_exists;
+
+--      type affirmation (this isn't the same as the implicit type created with the table)
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c text, d int);
+--      existence of type prevents finding the table
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP TYPE IF EXISTS test_rel_exists;
+
+--      view affirmation
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+--      existence of view prevents finding the table
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP VIEW test_rel_exists;
+
+--      index affirmation
+CREATE INDEX test_rel_exists ON test_if_exists_first.test_rel_with_index (ai);
+--      existence of index prevents finding the table
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP INDEX test_rel_exists;
+
+--      sequence affirmation
+CREATE SEQUENCE test_rel_exists;
+--      existence of sequence prevents finding the table
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP SEQUENCE test_rel_exists;
+
+--      materialized affirmation
+CREATE MATERIALIZED VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+--      existence of materialized view prevents finding the table
+DROP TABLE test_rel_exists;
+
+--      schema qualification works though (and cleanup)
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP MATERIALIZED VIEW test_rel_exists;
+DROP TABLE test_if_exists_first.test_rel_with_index;
+
+-- Type & Domain behavior is thus:
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      domain dropping errors with presence of table; no hint provided
+DROP DOMAIN IF EXISTS test_rel_exists;
+--      domain affirmation
+CREATE DOMAIN test_rel_exists int4;
+--      existence of domain in first search_path schema
+--      does not prevent second search_path table dropping
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP DOMAIN test_rel_exists;
+
+--      setup
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      type with same name exists as table creation creates a composite type
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+--      domain creation with same name as table fails as auto-generated type conflicts
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+--      cannot independently drop a composite type associated with a table
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+--      cleanup
+DROP TABLE test_if_exists_second.test_rel_exists;
+
+--      setup
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+--      auto-created type (which is added also as a relation) prevents table from being created
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      a composite type is not a domain so a conditional drop fails
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+--      can still create a domain in the first schema
+CREATE DOMAIN test_rel_exists int4;
+--      unlike the case with relations the fact that domains
+--      and other extensible types share the same namespace
+--      doesn't cause a DROP TYPE command that first
+--      finds a domain to fail - though it does prevent
+--      the search algorithm from looking in the second
+--      schema for an exact match.
+DROP TYPE IF EXISTS test_rel_exists; -- This removes the domain
+ --     type present, not a domain
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+--      Yep, domain seems to have been removed
+DROP TYPE IF EXISTS test_if_exists_first.test_rel_exists;
+--      Yep, domain removed, finding the type
+DROP DOMAIN test_rel_exists;
+--      cleanup
+DROP TYPE test_rel_exists;
+
+--      test with domain second and type first
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c int, d text);
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+--      fails since the first matched name is not a domain
+DROP DOMAIN IF EXISTS test_rel_exists;
+--      remove the matching type
+DROP TYPE IF EXISTS test_rel_exists;
+--      drop type cleans up domains...
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+--      ...so it no longer exists here
+DROP DOMAIN IF EXISTS test_rel_exists;
+-- /Type & Domain
+
+-- Bug # 16492 - this script produces an error, arguably it should not
+CREATE TABLE test_if_exists_first.test_rel_exists (a int, b text);
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP VIEW test_if_exists_first.test_rel_exists;
+-- /Bug # 16492
+
 -- This test checks both the functionality of 'if exists' and the syntax
 -- of the drop database command.
 drop database test_database_exists (force);

diff --git a/doc/src/sgml/glossary.sgml b/doc/src/sgml/glossary.sgml
index 76525c6302..1dac096f23 100644
--- a/doc/src/sgml/glossary.sgml
+++ b/doc/src/sgml/glossary.sgml
@@ -1689,6 +1689,30 @@
    </glossdef>
   </glossentry>
 
+  <glossentry id="glossary-type">
+   <glossterm>Type</glossterm>
+   <glossdef>
+    <para>
+     All data stored within the database is typed.  Each type has both a name, and associated
+     properties, as well as an overarching Type, of which there are two variations. Extensible
+     types can created by users and comprise of: base, composite, domain, enum, and range. There
+     are also the system-only pseudo-types.  Type records are stored in pg_type and the
+     overarching type is found in pg_type.typtype.
+    </para>
+   </glossdef>
+  </glossentry>  
+
+  <glossentry id="glossary-type-definition">
+   <glossterm>Type Definition</glossterm>
+   <glossdef>
+    <para>
+     Collective term for the various <glossterm linkend="glossary-type">Type</glossterm>
+     variants that are allowed for pg_type.typtype catalog table column values;
+     specifically, ones that are extensible.
+    </para>
+   </glossdef>
+  </glossentry>
+
   <glossentry id="glossary-unique-constraint">
    <glossterm>Unique constraint</glossterm>
    <glossdef>
diff --git a/doc/src/sgml/ref/drop_domain.sgml b/doc/src/sgml/ref/drop_domain.sgml
index b18faf3917..8b04b3818b 100644
--- a/doc/src/sgml/ref/drop_domain.sgml
+++ b/doc/src/sgml/ref/drop_domain.sgml
@@ -30,7 +30,9 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
 
   <para>
    <command>DROP DOMAIN</command> removes a domain.  Only the owner of
-   a domain can remove it.
+   a domain can remove it.  The duplicates the functionality provided by 
+   <xref linkend="sql-droptype"/> but restricts the object type to domain.
+
   </para>
  </refsect1>
 
@@ -42,8 +44,13 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the domain does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any 
+      <glossterm linkend="glossary-type-definition">type definition</glossterm>
+      with the provided name.
+      If no type definitions are found a notice is issued and the command ends.
+      If a type definition is found then one of two things will happen:
+      if the type definition is a domain it is dropped, otherwise the command fails.      
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_foreign_table.sgml b/doc/src/sgml/ref/drop_foreign_table.sgml
index 07b3fd4251..0288fb2062 100644
--- a/doc/src/sgml/ref/drop_foreign_table.sgml
+++ b/doc/src/sgml/ref/drop_foreign_table.sgml
@@ -42,8 +42,11 @@ DROP FOREIGN TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceabl
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the foreign table does not exist.
-      A notice is issued in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a foreign table it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_index.sgml b/doc/src/sgml/ref/drop_index.sgml
index 0aedd71bd6..dff437cf9b 100644
--- a/doc/src/sgml/ref/drop_index.sgml
+++ b/doc/src/sgml/ref/drop_index.sgml
@@ -70,8 +70,11 @@ DROP INDEX [ CONCURRENTLY ] [ IF EXISTS ] <replaceable class="parameter">name</r
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the index does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is an index it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_materialized_view.sgml b/doc/src/sgml/ref/drop_materialized_view.sgml
index c8f3bc5b0d..6647a0db0d 100644
--- a/doc/src/sgml/ref/drop_materialized_view.sgml
+++ b/doc/src/sgml/ref/drop_materialized_view.sgml
@@ -43,8 +43,11 @@ DROP MATERIALIZED VIEW [ IF EXISTS ] <replaceable class="parameter">name</replac
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the materialized view does not exist. A notice
-      is issued in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a materialized view it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_sequence.sgml b/doc/src/sgml/ref/drop_sequence.sgml
index 387c98edbc..b3209d6d01 100644
--- a/doc/src/sgml/ref/drop_sequence.sgml
+++ b/doc/src/sgml/ref/drop_sequence.sgml
@@ -42,8 +42,11 @@ DROP SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [,
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the sequence does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a sequence it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_table.sgml b/doc/src/sgml/ref/drop_table.sgml
index bf8996d198..9c9147f2ef 100644
--- a/doc/src/sgml/ref/drop_table.sgml
+++ b/doc/src/sgml/ref/drop_table.sgml
@@ -55,8 +55,11 @@ DROP TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ..
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the table does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a table it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_type.sgml b/doc/src/sgml/ref/drop_type.sgml
index 9e555c0624..305a62486f 100644
--- a/doc/src/sgml/ref/drop_type.sgml
+++ b/doc/src/sgml/ref/drop_type.sgml
@@ -42,8 +42,17 @@ DROP TYPE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the type does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any 
+      <glossterm linkend="glossary-type-definition">type definition</glossterm>
+      with the provided name.
+      If no type definitions are found a notice is issued and the command ends.
+      If a type definition is found then it will be dropped. This includes
+      domains even though they have their own drop command.
+      
+      However, an attempt to drop the automatically created composite type of an
+      existing relation will fail as the relation has a dependency on the found
+      type definition.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_view.sgml b/doc/src/sgml/ref/drop_view.sgml
index a1c550ec3e..ff75410cf1 100644
--- a/doc/src/sgml/ref/drop_view.sgml
+++ b/doc/src/sgml/ref/drop_view.sgml
@@ -42,8 +42,11 @@ DROP VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the view does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a view it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/test/regress/expected/drop_if_exists.out b/src/test/regress/expected/drop_if_exists.out
index 5e44c2c3ce..f328d94b9e 100644
--- a/src/test/regress/expected/drop_if_exists.out
+++ b/src/test/regress/expected/drop_if_exists.out
@@ -330,6 +330,167 @@ HINT:  Specify the argument list to select the routine unambiguously.
 -- cleanup
 DROP PROCEDURE test_ambiguous_procname(int);
 DROP PROCEDURE test_ambiguous_procname(text);
+-- Demonstrate namespace collision behavior
+CREATE SCHEMA test_if_exists_first;
+CREATE SCHEMA test_if_exists_second;
+SET search_path TO test_if_exists_first, test_if_exists_second;
+DROP TABLE test_if_exists_second.test_rel_exists;
+ERROR:  table "test_rel_exists" does not exist
+DROP TABLE IF EXISTS test_if_exists_second.test_rel_exists;
+NOTICE:  table "test_rel_exists" does not exist, skipping
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TABLE test_if_exists_first.test_rel_with_index (ai int, bi text);
+-- table presence in the second schema causes a failure here
+-- even though a corresponding non-schema-qualified create
+-- statement would succeed.
+DROP VIEW IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a view
+HINT:  Use DROP TABLE to remove a table.
+DROP INDEX IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not an index
+HINT:  Use DROP TABLE to remove a table.
+DROP TYPE IF EXISTS test_rel_exists;
+ERROR:  cannot drop type test_rel_exists because table test_rel_exists requires it
+HINT:  You can drop table test_rel_exists instead.
+DROP SEQUENCE IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a sequence
+HINT:  Use DROP TABLE to remove a table.
+DROP MATERIALIZED VIEW IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a materialized view
+HINT:  Use DROP TABLE to remove a table.
+DROP FOREIGN TABLE IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a foreign table
+HINT:  Use DROP TABLE to remove a table.
+-- a role is not a relation so this shouldn't be affected
+DROP ROLE IF EXISTS test_rel_exists;
+NOTICE:  role "test_rel_exists" does not exist, skipping
+--      type affirmation (this isn't the same as the implicit type created with the table)
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c text, d int);
+--      existence of type prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP TYPE to remove a type.
+--      cleanup
+DROP TYPE IF EXISTS test_rel_exists;
+--      view affirmation
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+--      existence of view prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP VIEW to remove a view.
+--      cleanup
+DROP VIEW test_rel_exists;
+--      index affirmation
+CREATE INDEX test_rel_exists ON test_if_exists_first.test_rel_with_index (ai);
+--      existence of index prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP INDEX to remove an index.
+--      cleanup
+DROP INDEX test_rel_exists;
+--      sequence affirmation
+CREATE SEQUENCE test_rel_exists;
+--      existence of sequence prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP SEQUENCE to remove a sequence.
+--      cleanup
+DROP SEQUENCE test_rel_exists;
+--      materialized affirmation
+CREATE MATERIALIZED VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+--      existence of materialized view prevents finding the table
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP MATERIALIZED VIEW to remove a materialized view.
+--      schema qualification works though (and cleanup)
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP MATERIALIZED VIEW test_rel_exists;
+DROP TABLE test_if_exists_first.test_rel_with_index;
+-- Type & Domain behavior is thus:
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      domain dropping errors with presence of table; no hint provided
+DROP DOMAIN IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+--      domain affirmation
+CREATE DOMAIN test_rel_exists int4;
+--      existence of domain in first search_path schema
+--      does not prevent second search_path table dropping
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP DOMAIN test_rel_exists;
+--      setup
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      type with same name exists as table creation creates a composite type
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+ERROR:  type "test_rel_exists" already exists
+--      domain creation with same name as table fails as auto-generated type conflicts
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+ERROR:  type "test_rel_exists" already exists
+--      cannot independently drop a composite type associated with a table
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  cannot drop type test_rel_exists because table test_rel_exists requires it
+HINT:  You can drop table test_rel_exists instead.
+--      cleanup
+DROP TABLE test_if_exists_second.test_rel_exists;
+--      setup
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+--      auto-created type (which is added also as a relation) prevents table from being created
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+ERROR:  relation "test_rel_exists" already exists
+--      a composite type is not a domain so a conditional drop fails
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  "test_if_exists_second.test_rel_exists" is not a domain
+--      can still create a domain in the first schema
+CREATE DOMAIN test_rel_exists int4;
+--      unlike the case with relations the fact that domains
+--      and other extensible types share the same namespace
+--      doesn't cause a DROP TYPE command that first
+--      finds a domain to fail - though it does prevent
+--      the search algorithm from looking in the second
+--      schema for an exact match.
+DROP TYPE IF EXISTS test_rel_exists; -- This removes the domain
+ --     type present, not a domain
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  "test_if_exists_second.test_rel_exists" is not a domain
+--      Yep, domain seems to have been removed
+DROP TYPE IF EXISTS test_if_exists_first.test_rel_exists;
+NOTICE:  type "test_if_exists_first.test_rel_exists" does not exist, skipping
+--      Yep, domain removed, finding the type
+DROP DOMAIN test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+--      cleanup
+DROP TYPE test_rel_exists;
+--      test with domain second and type first
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c int, d text);
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+--      fails since the first matched name is not a domain
+DROP DOMAIN IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+--      remove the matching type
+DROP TYPE IF EXISTS test_rel_exists;
+--      drop type cleans up domains...
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+--      ...so it no longer exists here
+DROP DOMAIN IF EXISTS test_rel_exists;
+NOTICE:  type "test_rel_exists" does not exist, skipping
+-- /Type & Domain
+-- Bug # 16492 - this script produces an error, arguably it should not
+CREATE TABLE test_if_exists_first.test_rel_exists (a int, b text);
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+NOTICE:  view "test_rel_exists" does not exist, skipping
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP VIEW to remove a view.
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP VIEW test_if_exists_first.test_rel_exists;
+-- /Bug # 16492
 -- This test checks both the functionality of 'if exists' and the syntax
 -- of the drop database command.
 drop database test_database_exists (force);
diff --git a/src/test/regress/sql/drop_if_exists.sql b/src/test/regress/sql/drop_if_exists.sql
index ac6168b91f..5cb7f17875 100644
--- a/src/test/regress/sql/drop_if_exists.sql
+++ b/src/test/regress/sql/drop_if_exists.sql
@@ -296,6 +296,142 @@ DROP ROUTINE IF EXISTS test_ambiguous_procname;
 DROP PROCEDURE test_ambiguous_procname(int);
 DROP PROCEDURE test_ambiguous_procname(text);
 
+-- Demonstrate namespace collision behavior
+CREATE SCHEMA test_if_exists_first;
+CREATE SCHEMA test_if_exists_second;
+SET search_path TO test_if_exists_first, test_if_exists_second;
+
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP TABLE IF EXISTS test_if_exists_second.test_rel_exists;
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TABLE test_if_exists_first.test_rel_with_index (ai int, bi text);
+
+-- table presence in the second schema causes a failure here
+-- even though a corresponding non-schema-qualified create
+-- statement would succeed.
+DROP VIEW IF EXISTS test_rel_exists;
+DROP INDEX IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_rel_exists;
+DROP SEQUENCE IF EXISTS test_rel_exists;
+DROP MATERIALIZED VIEW IF EXISTS test_rel_exists;
+DROP FOREIGN TABLE IF EXISTS test_rel_exists;
+
+-- a role is not a relation so this shouldn't be affected
+DROP ROLE IF EXISTS test_rel_exists;
+
+--      type affirmation (this isn't the same as the implicit type created with the table)
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c text, d int);
+--      existence of type prevents finding the table
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP TYPE IF EXISTS test_rel_exists;
+
+--      view affirmation
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+--      existence of view prevents finding the table
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP VIEW test_rel_exists;
+
+--      index affirmation
+CREATE INDEX test_rel_exists ON test_if_exists_first.test_rel_with_index (ai);
+--      existence of index prevents finding the table
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP INDEX test_rel_exists;
+
+--      sequence affirmation
+CREATE SEQUENCE test_rel_exists;
+--      existence of sequence prevents finding the table
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP SEQUENCE test_rel_exists;
+
+--      materialized affirmation
+CREATE MATERIALIZED VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+--      existence of materialized view prevents finding the table
+DROP TABLE test_rel_exists;
+
+--      schema qualification works though (and cleanup)
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP MATERIALIZED VIEW test_rel_exists;
+DROP TABLE test_if_exists_first.test_rel_with_index;
+
+-- Type & Domain behavior is thus:
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      domain dropping errors with presence of table; no hint provided
+DROP DOMAIN IF EXISTS test_rel_exists;
+--      domain affirmation
+CREATE DOMAIN test_rel_exists int4;
+--      existence of domain in first search_path schema
+--      does not prevent second search_path table dropping
+DROP TABLE test_rel_exists;
+--      cleanup
+DROP DOMAIN test_rel_exists;
+
+--      setup
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      type with same name exists as table creation creates a composite type
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+--      domain creation with same name as table fails as auto-generated type conflicts
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+--      cannot independently drop a composite type associated with a table
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+--      cleanup
+DROP TABLE test_if_exists_second.test_rel_exists;
+
+--      setup
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+--      auto-created type (which is added also as a relation) prevents table from being created
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+--      a composite type is not a domain so a conditional drop fails
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+--      can still create a domain in the first schema
+CREATE DOMAIN test_rel_exists int4;
+--      unlike the case with relations the fact that domains
+--      and other extensible types share the same namespace
+--      doesn't cause a DROP TYPE command that first
+--      finds a domain to fail - though it does prevent
+--      the search algorithm from looking in the second
+--      schema for an exact match.
+DROP TYPE IF EXISTS test_rel_exists; -- This removes the domain
+ --     type present, not a domain
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+--      Yep, domain seems to have been removed
+DROP TYPE IF EXISTS test_if_exists_first.test_rel_exists;
+--      Yep, domain removed, finding the type
+DROP DOMAIN test_rel_exists;
+--      cleanup
+DROP TYPE test_rel_exists;
+
+--      test with domain second and type first
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c int, d text);
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+--      fails since the first matched name is not a domain
+DROP DOMAIN IF EXISTS test_rel_exists;
+--      remove the matching type
+DROP TYPE IF EXISTS test_rel_exists;
+--      drop type cleans up domains...
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+--      ...so it no longer exists here
+DROP DOMAIN IF EXISTS test_rel_exists;
+-- /Type & Domain
+
+-- Bug # 16492 - this script produces an error, arguably it should not
+CREATE TABLE test_if_exists_first.test_rel_exists (a int, b text);
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP VIEW test_if_exists_first.test_rel_exists;
+-- /Bug # 16492
+
 -- This test checks both the functionality of 'if exists' and the syntax
 -- of the drop database command.
 drop database test_database_exists (force);

commit d0f11aa4f8efe8a18ed3ffa4368c7245cc3c8deb
Author: David G. Johnston <david.g.johnston@gmail.com>
Date:   Wed Jun 17 22:24:08 2020 +0000

    Document DROP relation and DROP type IF EXISTS namespace behavior
    
    Bug# 16492 takes offense to the fact that DROP VIEW IF EXISTS name
    errors if a table with the same name exists but a view with that
    name does not.  While I believe the bug has merit there is no
    consensus to actually fix the behavior to work as it is documented.
    Therefore, fix the documentation to match the behavior and encode
    that behavior in the regression tests.
    
    Due to the behavior of CREATE TABLE producing a composite type
    the behaviors for DROP TYPE and DROP DOMAIN are relevant here so
    add tests and documentation for those as well.  In particular
    document that DROP TYPE drops domains.
    
    One shortcoming tested here is that DROP IF EXISTS doesn't only
    look at the first search_path entry while CREATE IF NOT EXISTS
    will only consider the first search_path entry.
    
    As this patch addresses undocumented fundamental behavior for these
    commands backpatch to all supported versions.
    
    I (DGJ) have not tried to address the IMO confusing statement that
    "composite types are relations".  That material is better done against
    head only anyway as it should incorporate the newly created glossary.

diff --git a/doc/src/sgml/ref/drop_domain.sgml b/doc/src/sgml/ref/drop_domain.sgml
index b18faf3917..cba665fcc7 100644
--- a/doc/src/sgml/ref/drop_domain.sgml
+++ b/doc/src/sgml/ref/drop_domain.sgml
@@ -30,7 +30,9 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
 
   <para>
    <command>DROP DOMAIN</command> removes a domain.  Only the owner of
-   a domain can remove it.
+   a domain can remove it.  This duplicates the functionality provided by 
+   <xref linkend="sql-droptype"/> but restricts the object type to domain.
+
   </para>
  </refsect1>
 
@@ -42,8 +44,11 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the domain does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any type definition with the provided name.
+      If no type definition is found a notice is issued and the command ends.
+      If a type definition is found then one of two things will happen:
+      if the type definition is a domain it is dropped, otherwise the command fails.      
      </para>
     </listitem>
    </varlistentry>
@@ -108,6 +113,7 @@ DROP DOMAIN box;
   <simplelist type="inline">
    <member><xref linkend="sql-createdomain"/></member>
    <member><xref linkend="sql-alterdomain"/></member>
+   <member><xref linkend="sql-droptype"/></member>
   </simplelist>
  </refsect1>
 
diff --git a/doc/src/sgml/ref/drop_foreign_table.sgml b/doc/src/sgml/ref/drop_foreign_table.sgml
index 07b3fd4251..0288fb2062 100644
--- a/doc/src/sgml/ref/drop_foreign_table.sgml
+++ b/doc/src/sgml/ref/drop_foreign_table.sgml
@@ -42,8 +42,11 @@ DROP FOREIGN TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceabl
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the foreign table does not exist.
-      A notice is issued in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a foreign table it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_index.sgml b/doc/src/sgml/ref/drop_index.sgml
index 0aedd71bd6..dff437cf9b 100644
--- a/doc/src/sgml/ref/drop_index.sgml
+++ b/doc/src/sgml/ref/drop_index.sgml
@@ -70,8 +70,11 @@ DROP INDEX [ CONCURRENTLY ] [ IF EXISTS ] <replaceable class="parameter">name</r
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the index does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is an index it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_materialized_view.sgml b/doc/src/sgml/ref/drop_materialized_view.sgml
index c8f3bc5b0d..6647a0db0d 100644
--- a/doc/src/sgml/ref/drop_materialized_view.sgml
+++ b/doc/src/sgml/ref/drop_materialized_view.sgml
@@ -43,8 +43,11 @@ DROP MATERIALIZED VIEW [ IF EXISTS ] <replaceable class="parameter">name</replac
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the materialized view does not exist. A notice
-      is issued in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a materialized view it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_sequence.sgml b/doc/src/sgml/ref/drop_sequence.sgml
index 387c98edbc..b3209d6d01 100644
--- a/doc/src/sgml/ref/drop_sequence.sgml
+++ b/doc/src/sgml/ref/drop_sequence.sgml
@@ -42,8 +42,11 @@ DROP SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [,
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the sequence does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a sequence it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_table.sgml b/doc/src/sgml/ref/drop_table.sgml
index bf8996d198..9c9147f2ef 100644
--- a/doc/src/sgml/ref/drop_table.sgml
+++ b/doc/src/sgml/ref/drop_table.sgml
@@ -55,8 +55,11 @@ DROP TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ..
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the table does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a table it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_type.sgml b/doc/src/sgml/ref/drop_type.sgml
index 9e555c0624..afaa2387fe 100644
--- a/doc/src/sgml/ref/drop_type.sgml
+++ b/doc/src/sgml/ref/drop_type.sgml
@@ -30,7 +30,9 @@ DROP TYPE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
 
   <para>
    <command>DROP TYPE</command> removes a user-defined data type.
-   Only the owner of a type can remove it.
+   Only the owner of a type can remove it.  This includes domains,
+   though they can be targeted specifically by using the
+   <xref linkend="sql-dropdomain"/> command.
   </para>
  </refsect1>
 
@@ -42,8 +44,15 @@ DROP TYPE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the type does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any type definition with the provided name.
+      If no type definition is found a notice is issued and the command ends.
+      If a type definition is found then it will be dropped. 
+     </para>
+     <para> 
+      However, an attempt to drop the automatically created composite type of an
+      existing relation will fail as the relation has a dependency on the found
+      type definition.
      </para>
     </listitem>
    </varlistentry>
@@ -110,6 +119,7 @@ DROP TYPE box;
   <simplelist type="inline">
    <member><xref linkend="sql-altertype"/></member>
    <member><xref linkend="sql-createtype"/></member>
+   <member><xref linkend="sql-dropdomain"/></member>
   </simplelist>
  </refsect1>
 
diff --git a/doc/src/sgml/ref/drop_view.sgml b/doc/src/sgml/ref/drop_view.sgml
index a1c550ec3e..ff75410cf1 100644
--- a/doc/src/sgml/ref/drop_view.sgml
+++ b/doc/src/sgml/ref/drop_view.sgml
@@ -42,8 +42,11 @@ DROP VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the view does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a view it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/test/regress/expected/drop_if_exists.out b/src/test/regress/expected/drop_if_exists.out
index 5e44c2c3ce..b25886272b 100644
--- a/src/test/regress/expected/drop_if_exists.out
+++ b/src/test/regress/expected/drop_if_exists.out
@@ -330,6 +330,125 @@ HINT:  Specify the argument list to select the routine unambiguously.
 -- cleanup
 DROP PROCEDURE test_ambiguous_procname(int);
 DROP PROCEDURE test_ambiguous_procname(text);
+-- ============== Demonstrate namespace collision behavior =======
+CREATE SCHEMA test_if_exists_first;
+CREATE SCHEMA test_if_exists_second;
+SET search_path TO test_if_exists_first, test_if_exists_second;
+DROP TABLE test_if_exists_second.test_rel_exists;
+ERROR:  table "test_rel_exists" does not exist
+DROP TABLE IF EXISTS test_if_exists_second.test_rel_exists;
+NOTICE:  table "test_rel_exists" does not exist, skipping
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TABLE test_if_exists_first.test_rel_with_index (ai int, bi text);
+CREATE TABLE IF NOT EXISTS test_rel_exists (c text, d int); -- IF NOT EXISTS checks only the first schema
+DROP TABLE IF EXISTS test_rel_exists; -- Two matches but only the first is dropped
+-- A role is not a relation so this shouldn't be affected
+DROP ROLE IF EXISTS test_rel_exists;
+NOTICE:  role "test_rel_exists" does not exist, skipping
+-- Table presence in the second schema causes a failure here
+-- even though a corresponding non-schema-qualified create
+-- statement would succeed.
+DROP VIEW IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a view
+HINT:  Use DROP TABLE to remove a table.
+DROP INDEX IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not an index
+HINT:  Use DROP TABLE to remove a table.
+DROP SEQUENCE IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a sequence
+HINT:  Use DROP TABLE to remove a table.
+DROP MATERIALIZED VIEW IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a materialized view
+HINT:  Use DROP TABLE to remove a table.
+DROP FOREIGN TABLE IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a foreign table
+HINT:  Use DROP TABLE to remove a table.
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP VIEW to remove a view.
+DROP VIEW test_rel_exists;
+CREATE INDEX test_rel_exists ON test_if_exists_first.test_rel_with_index (ai);
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP INDEX to remove an index.
+DROP INDEX test_rel_exists;
+CREATE SEQUENCE test_rel_exists;
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP SEQUENCE to remove a sequence.
+DROP SEQUENCE test_rel_exists;
+CREATE MATERIALIZED VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP MATERIALIZED VIEW to remove a materialized view.
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP MATERIALIZED VIEW test_rel_exists;
+DROP TABLE test_if_exists_first.test_rel_with_index;
+-- Type & Domain behavior is thus:
+-- If Exists Behavior
+DROP DOMAIN IF EXISTS test_rel_exists;
+NOTICE:  type "test_rel_exists" does not exist, skipping
+DROP TYPE IF EXISTS test_rel_exists;
+NOTICE:  type "test_rel_exists" does not exist, skipping
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+DROP DOMAIN IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+CREATE DOMAIN test_rel_exists int4;
+DROP TABLE test_rel_exists;
+DROP DOMAIN test_rel_exists;
+-- Test with domain first and type second; plus table tests
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text); -- type with same name exists as table creation creates a composite type
+ERROR:  type "test_rel_exists" already exists
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4; -- domain creation with same name as table fails as auto-generated type conflicts
+ERROR:  type "test_rel_exists" already exists
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists; -- cannot independently drop a composite type associated with a table
+ERROR:  cannot drop type test_rel_exists because table test_rel_exists requires it
+HINT:  You can drop table test_rel_exists instead.
+DROP TABLE test_if_exists_second.test_rel_exists;
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text); -- auto-created type prevents table from being created
+ERROR:  relation "test_rel_exists" already exists
+DROP TABLE test_if_exists_second.test_rel_exists; -- a standalone composite type cannot be dropped using the drop table command
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP TYPE to remove a type.
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  "test_if_exists_second.test_rel_exists" is not a domain
+CREATE DOMAIN test_rel_exists int4;
+DROP TYPE IF EXISTS test_rel_exists; -- DROP TYPE Drops the Domain
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  "test_if_exists_second.test_rel_exists" is not a domain
+DROP DOMAIN test_rel_exists; -- double-checking the domain doesn't exist
+ERROR:  "test_rel_exists" is not a domain
+DROP TYPE test_rel_exists;
+-- Test with domain second and type first
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c int, d text);
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+DROP DOMAIN IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+DROP TYPE IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+DROP DOMAIN IF EXISTS test_rel_exists;
+NOTICE:  type "test_rel_exists" does not exist, skipping
+-- /Type & Domain
+-- Bug # 16492 - this script produces an error, arguably it should not
+CREATE TABLE test_if_exists_first.test_rel_exists (a int, b text);
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+NOTICE:  view "test_rel_exists" does not exist, skipping
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP VIEW to remove a view.
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP VIEW test_if_exists_first.test_rel_exists;
+-- /Bug # 16492
 -- This test checks both the functionality of 'if exists' and the syntax
 -- of the drop database command.
 drop database test_database_exists (force);
diff --git a/src/test/regress/sql/drop_if_exists.sql b/src/test/regress/sql/drop_if_exists.sql
index ac6168b91f..b95189c47c 100644
--- a/src/test/regress/sql/drop_if_exists.sql
+++ b/src/test/regress/sql/drop_if_exists.sql
@@ -296,6 +296,104 @@ DROP ROUTINE IF EXISTS test_ambiguous_procname;
 DROP PROCEDURE test_ambiguous_procname(int);
 DROP PROCEDURE test_ambiguous_procname(text);
 
+-- ============== Demonstrate namespace collision behavior =======
+CREATE SCHEMA test_if_exists_first;
+CREATE SCHEMA test_if_exists_second;
+SET search_path TO test_if_exists_first, test_if_exists_second;
+
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP TABLE IF EXISTS test_if_exists_second.test_rel_exists;
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TABLE test_if_exists_first.test_rel_with_index (ai int, bi text);
+
+CREATE TABLE IF NOT EXISTS test_rel_exists (c text, d int); -- IF NOT EXISTS checks only the first schema
+DROP TABLE IF EXISTS test_rel_exists; -- Two matches but only the first is dropped
+
+-- A role is not a relation so this shouldn't be affected
+DROP ROLE IF EXISTS test_rel_exists;
+
+-- Table presence in the second schema causes a failure here
+-- even though a corresponding non-schema-qualified create
+-- statement would succeed.
+DROP VIEW IF EXISTS test_rel_exists;
+DROP INDEX IF EXISTS test_rel_exists;
+DROP SEQUENCE IF EXISTS test_rel_exists;
+DROP MATERIALIZED VIEW IF EXISTS test_rel_exists;
+DROP FOREIGN TABLE IF EXISTS test_rel_exists;
+
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+DROP TABLE test_rel_exists;
+DROP VIEW test_rel_exists;
+
+CREATE INDEX test_rel_exists ON test_if_exists_first.test_rel_with_index (ai);
+DROP TABLE test_rel_exists;
+DROP INDEX test_rel_exists;
+
+CREATE SEQUENCE test_rel_exists;
+DROP TABLE test_rel_exists;
+DROP SEQUENCE test_rel_exists;
+
+CREATE MATERIALIZED VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+DROP TABLE test_rel_exists;
+
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP MATERIALIZED VIEW test_rel_exists;
+DROP TABLE test_if_exists_first.test_rel_with_index;
+
+-- Type & Domain behavior is thus:
+-- If Exists Behavior
+DROP DOMAIN IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_rel_exists;
+
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+DROP DOMAIN IF EXISTS test_rel_exists;
+CREATE DOMAIN test_rel_exists int4;
+DROP TABLE test_rel_exists;
+DROP DOMAIN test_rel_exists;
+
+-- Test with domain first and type second; plus table tests
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text); -- type with same name exists as table creation creates a composite type
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4; -- domain creation with same name as table fails as auto-generated type conflicts
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists; -- cannot independently drop a composite type associated with a table
+DROP TABLE test_if_exists_second.test_rel_exists;
+
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text); -- auto-created type prevents table from being created
+DROP TABLE test_if_exists_second.test_rel_exists; -- a standalone composite type cannot be dropped using the drop table command
+
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+CREATE DOMAIN test_rel_exists int4;
+DROP TYPE IF EXISTS test_rel_exists; -- DROP TYPE Drops the Domain
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+DROP DOMAIN test_rel_exists; -- double-checking the domain doesn't exist
+DROP TYPE test_rel_exists;
+
+-- Test with domain second and type first
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c int, d text);
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+DROP DOMAIN IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+
+DROP DOMAIN IF EXISTS test_rel_exists;
+-- /Type & Domain
+
+-- Bug # 16492 - this script produces an error, arguably it should not
+CREATE TABLE test_if_exists_first.test_rel_exists (a int, b text);
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP VIEW test_if_exists_first.test_rel_exists;
+-- /Bug # 16492
+
 -- This test checks both the functionality of 'if exists' and the syntax
 -- of the drop database command.
 drop database test_database_exists (force);

commit 508dc751e2ed60e9ba6bb4849e9320543ae0f134
Author: David G. Johnston <david.g.johnston@gmail.com>
Date:   Tue Jul 14 15:38:30 2020 +0000

    Link CREATE/DROP TYPE and DOMAIN to the Glossary
    
    We have a generic term that encompasses tables, views, etc...,
    "relation".  Introduce the term "type definition" to encompass
    base, composite, domain, etc... types.  The individual types
    are the rows on pg_type while type definition represents the
    allowed values for the pg_type.typtype column (restricted to
    user-creatable ones).
    
    Update the TYPE and DOMAIN pages to refer to these
    glossary entries.

diff --git a/doc/src/sgml/glossary.sgml b/doc/src/sgml/glossary.sgml
index 25b03f3b37..c517ff5b4a 100644
--- a/doc/src/sgml/glossary.sgml
+++ b/doc/src/sgml/glossary.sgml
@@ -1612,6 +1612,30 @@
    </glossdef>
   </glossentry>
 
+  <glossentry id="glossary-type">
+   <glossterm>Type</glossterm>
+   <glossdef>
+    <para>
+     All data stored within the database is typed.  Each type has both a name, and associated
+     properties, as well as an overarching Type, of which there are two variations. Extensible
+     types can created by users and comprise of: base, composite, domain, enum, and range. There
+     are also the system-only pseudo-types.  Type records are stored in pg_type and the
+     overarching type is found in pg_type.typtype.
+    </para>
+   </glossdef>
+  </glossentry>  
+
+  <glossentry id="glossary-type-definition">
+   <glossterm>Type Definition</glossterm>
+   <glossdef>
+    <para>
+     Collective term for the various <glossterm linkend="glossary-type">Type</glossterm>
+     variants that are allowed for pg_type.typtype catalog table column values;
+     specifically, ones that are extensible.
+    </para>
+   </glossdef>
+  </glossentry>
+
   <glossentry id="glossary-unique-constraint">
    <glossterm>Unique constraint</glossterm>
    <glossdef>
diff --git a/doc/src/sgml/ref/create_domain.sgml b/doc/src/sgml/ref/create_domain.sgml
index 81a8924926..00e1544ac8 100644
--- a/doc/src/sgml/ref/create_domain.sgml
+++ b/doc/src/sgml/ref/create_domain.sgml
@@ -38,8 +38,8 @@ CREATE DOMAIN <replaceable class="parameter">name</replaceable> [ AS ] <replacea
 
   <para>
    <command>CREATE DOMAIN</command> creates a new domain.  A domain is
-   essentially a data type with optional constraints (restrictions on
-   the allowed set of values).
+   essentially a data <glossterm linkend="glossary-type">type</glossterm>
+   with optional constraints (restrictions on the allowed set of values).
    The user who defines a domain becomes its owner.
   </para>
 
@@ -64,6 +64,13 @@ CREATE DOMAIN <replaceable class="parameter">name</replaceable> [ AS ] <replacea
    To be able to create a domain, you must have <literal>USAGE</literal>
    privilege on the underlying type.
   </para>
+  
+  <para>
+   This emulates the functionality provided by 
+   <xref linkend="sql-createtype"/> but sets the created object's
+   <glossterm linkend="glossary-type-definition">type definition</glossterm>
+   to domain.
+  </para>
  </refsect1>
 
  <refsect1>
diff --git a/doc/src/sgml/ref/create_type.sgml b/doc/src/sgml/ref/create_type.sgml
index 111f8e65d2..bbeeca7317 100644
--- a/doc/src/sgml/ref/create_type.sgml
+++ b/doc/src/sgml/ref/create_type.sgml
@@ -64,9 +64,10 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
   <title>Description</title>
 
   <para>
-   <command>CREATE TYPE</command> registers a new data type for use in
-   the current database.  The user who defines a type becomes its
-   owner.
+   <command>CREATE TYPE</command> registers a new data
+   <glossterm linkend="glossary-type">type</glossterm>
+   for use in the current database.  The user who defines
+   a type becomes its owner.
   </para>
 
   <para>
@@ -83,7 +84,10 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
    syntax synopsis above.  They respectively create a <firstterm>composite
    type</firstterm>, an <firstterm>enum type</firstterm>, a <firstterm>range type</firstterm>, a
    <firstterm>base type</firstterm>, or a <firstterm>shell type</firstterm>.  The first four
-   of these are discussed in turn below.  A shell type is simply a placeholder
+   of these are discussed in turn below and represent four of the five
+   <glossterm linkend="glossary-type-definition">type definition</glossterm>s,
+   with the fifth, domain, created using the <xref linkend="sql-createdomain"/> command.
+   A shell type is simply a placeholder
    for a type to be defined later; it is created by issuing <command>CREATE
    TYPE</command> with no parameters except for the type name.  Shell types
    are needed as forward references when creating range types and base types,
diff --git a/doc/src/sgml/ref/drop_domain.sgml b/doc/src/sgml/ref/drop_domain.sgml
index cba665fcc7..8375dd5849 100644
--- a/doc/src/sgml/ref/drop_domain.sgml
+++ b/doc/src/sgml/ref/drop_domain.sgml
@@ -29,10 +29,13 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
   <title>Description</title>
 
   <para>
-   <command>DROP DOMAIN</command> removes a domain.  Only the owner of
-   a domain can remove it.  This duplicates the functionality provided by 
-   <xref linkend="sql-droptype"/> but restricts the object type to domain.
-
+   <command>DROP DOMAIN</command> removes a domain
+   <glossterm linkend="glossary-type">type</glossterm>.
+   Only the owner of a domain can remove it.
+   This duplicates the functionality provided by 
+   <xref linkend="sql-droptype"/> but restricts the object
+   <glossterm linkend="glossary-type-definition">type definition</glossterm>
+   to domain.
   </para>
  </refsect1>
 
@@ -45,7 +48,9 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
     <listitem>
      <para>
       This parameter instructs <productname>PostgreSQL</productname> to search 
-      for the first instance of any type definition with the provided name.
+      for the first instance of any
+      <glossterm linkend="glossary-type-definition">type definition</glossterm>
+      with the provided name.
       If no type definition is found a notice is issued and the command ends.
       If a type definition is found then one of two things will happen:
       if the type definition is a domain it is dropped, otherwise the command fails.      
diff --git a/doc/src/sgml/ref/drop_type.sgml b/doc/src/sgml/ref/drop_type.sgml
index afaa2387fe..393be721e3 100644
--- a/doc/src/sgml/ref/drop_type.sgml
+++ b/doc/src/sgml/ref/drop_type.sgml
@@ -29,10 +29,11 @@ DROP TYPE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
   <title>Description</title>
 
   <para>
-   <command>DROP TYPE</command> removes a user-defined data type.
-   Only the owner of a type can remove it.  This includes domains,
-   though they can be targeted specifically by using the
-   <xref linkend="sql-dropdomain"/> command.
+   <command>DROP TYPE</command> removes a user-defined data
+   <glossterm linkend="glossary-type">type</glossterm>.
+   Only the owner of a type can remove it.
+   This includes domains, though they can be targeted
+   specifically by using the <xref linkend="sql-dropdomain"/> command.
   </para>
  </refsect1>
 
@@ -45,7 +46,9 @@ DROP TYPE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <listitem>
      <para>
       This parameter instructs <productname>PostgreSQL</productname> to search 
-      for the first instance of any type definition with the provided name.
+      for the first instance of any 
+      <glossterm linkend="glossary-type-definition">type definition</glossterm>
+      with the provided name.
       If no type definition is found a notice is issued and the command ends.
       If a type definition is found then it will be dropped. 
      </para>

commit 59ac2f05f66906e3cba20351e4d3b32f1d635e29
Author: David G. Johnston <david.g.johnston@gmail.com>
Date:   Wed Sep 30 01:51:20 2020 +0000

    Document DROP relation and DROP type IF EXISTS namespace behavior
    
    Bug# 16492 takes offense to the fact that DROP VIEW IF EXISTS name
    errors if a table with the same name exists but a view with that
    name does not.  While I believe the bug has merit there is no
    consensus to actually fix the behavior to work as it is documented.
    Therefore, fix the documentation to match the behavior and encode
    that behavior in the regression tests.
    
    Due to the behavior of CREATE TABLE producing a composite type
    the behaviors for DROP TYPE and DROP DOMAIN are relevant here so
    add tests and documentation for those as well.  In particular
    document that DROP TYPE drops domains.
    
    One shortcoming tested here is that DROP IF EXISTS doesn't only
    look at the first search_path entry while CREATE IF NOT EXISTS
    will only consider the first search_path entry.
    
    As this patch addresses undocumented fundamental behavior for these
    commands backpatch to all supported versions.

diff --git a/doc/src/sgml/ref/create_domain.sgml b/doc/src/sgml/ref/create_domain.sgml
index 81a8924926..612580c749 100644
--- a/doc/src/sgml/ref/create_domain.sgml
+++ b/doc/src/sgml/ref/create_domain.sgml
@@ -38,7 +38,7 @@ CREATE DOMAIN <replaceable class="parameter">name</replaceable> [ AS ] <replacea
 
   <para>
    <command>CREATE DOMAIN</command> creates a new domain.  A domain is
-   essentially a data type with optional constraints (restrictions on
+   a data type with optional constraints (restrictions on
    the allowed set of values).
    The user who defines a domain becomes its owner.
   </para>
@@ -47,8 +47,8 @@ CREATE DOMAIN <replaceable class="parameter">name</replaceable> [ AS ] <replacea
    If a schema name is given (for example, <literal>CREATE DOMAIN
    myschema.mydomain ...</literal>) then the domain is created in the
    specified schema.  Otherwise it is created in the current schema.
-   The domain name must be unique among the types and domains existing
-   in its schema.
+   The domain name must be unique among all types (not just domains)
+   existing in its schema.
   </para>
 
   <para>
@@ -281,6 +281,7 @@ CREATE TABLE us_snail_addy (
   <simplelist type="inline">
    <member><xref linkend="sql-alterdomain"/></member>
    <member><xref linkend="sql-dropdomain"/></member>
+   <member><xref linkend="sql-droptype"/></member>
   </simplelist>
  </refsect1>
 
diff --git a/doc/src/sgml/ref/create_type.sgml b/doc/src/sgml/ref/create_type.sgml
index 111f8e65d2..fe1bfe5906 100644
--- a/doc/src/sgml/ref/create_type.sgml
+++ b/doc/src/sgml/ref/create_type.sgml
@@ -72,8 +72,8 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
   <para>
    If a schema name is given then the type is created in the specified
    schema.  Otherwise it is created in the current schema.  The type
-   name must be distinct from the name of any existing type or domain
-   in the same schema.  (Because tables have associated data types,
+   name must be distinct from the name of any existing type (including
+   domains) in the same schema.  (Because tables have associated data types,
    the type name must also be distinct from the name of any existing
    table in the same schema.)
   </para>
@@ -83,7 +83,10 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
    syntax synopsis above.  They respectively create a <firstterm>composite
    type</firstterm>, an <firstterm>enum type</firstterm>, a <firstterm>range type</firstterm>, a
    <firstterm>base type</firstterm>, or a <firstterm>shell type</firstterm>.  The first four
-   of these are discussed in turn below.  A shell type is simply a placeholder
+   of these are discussed in turn below and represent four of the five types of data types,
+   with the fifth, a <firstterm>domain type</firstterm>, created using the
+   <xref linkend="sql-createdomain"/> command.
+   A shell type is simply a placeholder
    for a type to be defined later; it is created by issuing <command>CREATE
    TYPE</command> with no parameters except for the type name.  Shell types
    are needed as forward references when creating range types and base types,
diff --git a/doc/src/sgml/ref/drop_domain.sgml b/doc/src/sgml/ref/drop_domain.sgml
index b18faf3917..9106838c68 100644
--- a/doc/src/sgml/ref/drop_domain.sgml
+++ b/doc/src/sgml/ref/drop_domain.sgml
@@ -29,8 +29,11 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
   <title>Description</title>
 
   <para>
-   <command>DROP DOMAIN</command> removes a domain.  Only the owner of
-   a domain can remove it.
+   <command>DROP DOMAIN</command> removes a domain type.
+   Only the owner of a domain can remove it.
+   This duplicates the functionality provided by 
+   <xref linkend="sql-droptype"/> but restricts
+   the type's type to domain.
   </para>
  </refsect1>
 
@@ -42,8 +45,11 @@ DROP DOMAIN [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the domain does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any type with the provided name.
+      If no type is found a notice is issued and the command ends.
+      If a type is found then one of two things will happen:
+      if the type is a domain it is dropped, otherwise the command fails.      
      </para>
     </listitem>
    </varlistentry>
@@ -108,6 +114,7 @@ DROP DOMAIN box;
   <simplelist type="inline">
    <member><xref linkend="sql-createdomain"/></member>
    <member><xref linkend="sql-alterdomain"/></member>
+   <member><xref linkend="sql-droptype"/></member>
   </simplelist>
  </refsect1>
 
diff --git a/doc/src/sgml/ref/drop_foreign_table.sgml b/doc/src/sgml/ref/drop_foreign_table.sgml
index 07b3fd4251..0288fb2062 100644
--- a/doc/src/sgml/ref/drop_foreign_table.sgml
+++ b/doc/src/sgml/ref/drop_foreign_table.sgml
@@ -42,8 +42,11 @@ DROP FOREIGN TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceabl
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the foreign table does not exist.
-      A notice is issued in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a foreign table it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_index.sgml b/doc/src/sgml/ref/drop_index.sgml
index 85cf23bca2..b07627fb55 100644
--- a/doc/src/sgml/ref/drop_index.sgml
+++ b/doc/src/sgml/ref/drop_index.sgml
@@ -72,8 +72,11 @@ DROP INDEX [ CONCURRENTLY ] [ IF EXISTS ] <replaceable class="parameter">name</r
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the index does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is an index it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_materialized_view.sgml b/doc/src/sgml/ref/drop_materialized_view.sgml
index c8f3bc5b0d..6647a0db0d 100644
--- a/doc/src/sgml/ref/drop_materialized_view.sgml
+++ b/doc/src/sgml/ref/drop_materialized_view.sgml
@@ -43,8 +43,11 @@ DROP MATERIALIZED VIEW [ IF EXISTS ] <replaceable class="parameter">name</replac
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the materialized view does not exist. A notice
-      is issued in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a materialized view it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_sequence.sgml b/doc/src/sgml/ref/drop_sequence.sgml
index 387c98edbc..b3209d6d01 100644
--- a/doc/src/sgml/ref/drop_sequence.sgml
+++ b/doc/src/sgml/ref/drop_sequence.sgml
@@ -42,8 +42,11 @@ DROP SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [,
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the sequence does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a sequence it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_table.sgml b/doc/src/sgml/ref/drop_table.sgml
index bf8996d198..9c9147f2ef 100644
--- a/doc/src/sgml/ref/drop_table.sgml
+++ b/doc/src/sgml/ref/drop_table.sgml
@@ -55,8 +55,11 @@ DROP TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ..
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the table does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a table it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/drop_type.sgml b/doc/src/sgml/ref/drop_type.sgml
index 9e555c0624..f88e6353ee 100644
--- a/doc/src/sgml/ref/drop_type.sgml
+++ b/doc/src/sgml/ref/drop_type.sgml
@@ -31,6 +31,8 @@ DROP TYPE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
   <para>
    <command>DROP TYPE</command> removes a user-defined data type.
    Only the owner of a type can remove it.
+   This includes domains, though they can be removed specifically
+   by using the <xref linkend="sql-dropdomain"/> command.
   </para>
  </refsect1>
 
@@ -42,8 +44,15 @@ DROP TYPE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the type does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search
+      for the first instance of any type with the provided name.
+      If no type is found a notice is issued and the command ends.
+      If a type is found it is dropped.
+     </para>
+     <para>
+      However, dropping the automatically created composite type of an
+      existing relation will fail as the relation has a dependency on the composite
+      type.
      </para>
     </listitem>
    </varlistentry>
@@ -110,6 +119,7 @@ DROP TYPE box;
   <simplelist type="inline">
    <member><xref linkend="sql-altertype"/></member>
    <member><xref linkend="sql-createtype"/></member>
+   <member><xref linkend="sql-dropdomain"/></member>
   </simplelist>
  </refsect1>
 
diff --git a/doc/src/sgml/ref/drop_view.sgml b/doc/src/sgml/ref/drop_view.sgml
index a1c550ec3e..ff75410cf1 100644
--- a/doc/src/sgml/ref/drop_view.sgml
+++ b/doc/src/sgml/ref/drop_view.sgml
@@ -42,8 +42,11 @@ DROP VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, ...
     <term><literal>IF EXISTS</literal></term>
     <listitem>
      <para>
-      Do not throw an error if the view does not exist. A notice is issued
-      in this case.
+      This parameter instructs <productname>PostgreSQL</productname> to search 
+      for the first instance of any relation with the provided name.
+      If no relations are found a notice is issued and the command ends.
+      If a relation is found then one of two things will happen:
+      if the relation is a view it is dropped, otherwise the command fails.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/test/regress/expected/drop_if_exists.out b/src/test/regress/expected/drop_if_exists.out
index 5e44c2c3ce..b25886272b 100644
--- a/src/test/regress/expected/drop_if_exists.out
+++ b/src/test/regress/expected/drop_if_exists.out
@@ -330,6 +330,125 @@ HINT:  Specify the argument list to select the routine unambiguously.
 -- cleanup
 DROP PROCEDURE test_ambiguous_procname(int);
 DROP PROCEDURE test_ambiguous_procname(text);
+-- ============== Demonstrate namespace collision behavior =======
+CREATE SCHEMA test_if_exists_first;
+CREATE SCHEMA test_if_exists_second;
+SET search_path TO test_if_exists_first, test_if_exists_second;
+DROP TABLE test_if_exists_second.test_rel_exists;
+ERROR:  table "test_rel_exists" does not exist
+DROP TABLE IF EXISTS test_if_exists_second.test_rel_exists;
+NOTICE:  table "test_rel_exists" does not exist, skipping
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TABLE test_if_exists_first.test_rel_with_index (ai int, bi text);
+CREATE TABLE IF NOT EXISTS test_rel_exists (c text, d int); -- IF NOT EXISTS checks only the first schema
+DROP TABLE IF EXISTS test_rel_exists; -- Two matches but only the first is dropped
+-- A role is not a relation so this shouldn't be affected
+DROP ROLE IF EXISTS test_rel_exists;
+NOTICE:  role "test_rel_exists" does not exist, skipping
+-- Table presence in the second schema causes a failure here
+-- even though a corresponding non-schema-qualified create
+-- statement would succeed.
+DROP VIEW IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a view
+HINT:  Use DROP TABLE to remove a table.
+DROP INDEX IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not an index
+HINT:  Use DROP TABLE to remove a table.
+DROP SEQUENCE IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a sequence
+HINT:  Use DROP TABLE to remove a table.
+DROP MATERIALIZED VIEW IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a materialized view
+HINT:  Use DROP TABLE to remove a table.
+DROP FOREIGN TABLE IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a foreign table
+HINT:  Use DROP TABLE to remove a table.
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP VIEW to remove a view.
+DROP VIEW test_rel_exists;
+CREATE INDEX test_rel_exists ON test_if_exists_first.test_rel_with_index (ai);
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP INDEX to remove an index.
+DROP INDEX test_rel_exists;
+CREATE SEQUENCE test_rel_exists;
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP SEQUENCE to remove a sequence.
+DROP SEQUENCE test_rel_exists;
+CREATE MATERIALIZED VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+DROP TABLE test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP MATERIALIZED VIEW to remove a materialized view.
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP MATERIALIZED VIEW test_rel_exists;
+DROP TABLE test_if_exists_first.test_rel_with_index;
+-- Type & Domain behavior is thus:
+-- If Exists Behavior
+DROP DOMAIN IF EXISTS test_rel_exists;
+NOTICE:  type "test_rel_exists" does not exist, skipping
+DROP TYPE IF EXISTS test_rel_exists;
+NOTICE:  type "test_rel_exists" does not exist, skipping
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+DROP DOMAIN IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+CREATE DOMAIN test_rel_exists int4;
+DROP TABLE test_rel_exists;
+DROP DOMAIN test_rel_exists;
+-- Test with domain first and type second; plus table tests
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text); -- type with same name exists as table creation creates a composite type
+ERROR:  type "test_rel_exists" already exists
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4; -- domain creation with same name as table fails as auto-generated type conflicts
+ERROR:  type "test_rel_exists" already exists
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists; -- cannot independently drop a composite type associated with a table
+ERROR:  cannot drop type test_rel_exists because table test_rel_exists requires it
+HINT:  You can drop table test_rel_exists instead.
+DROP TABLE test_if_exists_second.test_rel_exists;
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text); -- auto-created type prevents table from being created
+ERROR:  relation "test_rel_exists" already exists
+DROP TABLE test_if_exists_second.test_rel_exists; -- a standalone composite type cannot be dropped using the drop table command
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP TYPE to remove a type.
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  "test_if_exists_second.test_rel_exists" is not a domain
+CREATE DOMAIN test_rel_exists int4;
+DROP TYPE IF EXISTS test_rel_exists; -- DROP TYPE Drops the Domain
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+ERROR:  "test_if_exists_second.test_rel_exists" is not a domain
+DROP DOMAIN test_rel_exists; -- double-checking the domain doesn't exist
+ERROR:  "test_rel_exists" is not a domain
+DROP TYPE test_rel_exists;
+-- Test with domain second and type first
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c int, d text);
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+DROP DOMAIN IF EXISTS test_rel_exists;
+ERROR:  "test_rel_exists" is not a domain
+DROP TYPE IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+DROP DOMAIN IF EXISTS test_rel_exists;
+NOTICE:  type "test_rel_exists" does not exist, skipping
+-- /Type & Domain
+-- Bug # 16492 - this script produces an error, arguably it should not
+CREATE TABLE test_if_exists_first.test_rel_exists (a int, b text);
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+NOTICE:  view "test_rel_exists" does not exist, skipping
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+ERROR:  "test_rel_exists" is not a table
+HINT:  Use DROP VIEW to remove a view.
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP VIEW test_if_exists_first.test_rel_exists;
+-- /Bug # 16492
 -- This test checks both the functionality of 'if exists' and the syntax
 -- of the drop database command.
 drop database test_database_exists (force);
diff --git a/src/test/regress/sql/drop_if_exists.sql b/src/test/regress/sql/drop_if_exists.sql
index ac6168b91f..b95189c47c 100644
--- a/src/test/regress/sql/drop_if_exists.sql
+++ b/src/test/regress/sql/drop_if_exists.sql
@@ -296,6 +296,104 @@ DROP ROUTINE IF EXISTS test_ambiguous_procname;
 DROP PROCEDURE test_ambiguous_procname(int);
 DROP PROCEDURE test_ambiguous_procname(text);
 
+-- ============== Demonstrate namespace collision behavior =======
+CREATE SCHEMA test_if_exists_first;
+CREATE SCHEMA test_if_exists_second;
+SET search_path TO test_if_exists_first, test_if_exists_second;
+
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP TABLE IF EXISTS test_if_exists_second.test_rel_exists;
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TABLE test_if_exists_first.test_rel_with_index (ai int, bi text);
+
+CREATE TABLE IF NOT EXISTS test_rel_exists (c text, d int); -- IF NOT EXISTS checks only the first schema
+DROP TABLE IF EXISTS test_rel_exists; -- Two matches but only the first is dropped
+
+-- A role is not a relation so this shouldn't be affected
+DROP ROLE IF EXISTS test_rel_exists;
+
+-- Table presence in the second schema causes a failure here
+-- even though a corresponding non-schema-qualified create
+-- statement would succeed.
+DROP VIEW IF EXISTS test_rel_exists;
+DROP INDEX IF EXISTS test_rel_exists;
+DROP SEQUENCE IF EXISTS test_rel_exists;
+DROP MATERIALIZED VIEW IF EXISTS test_rel_exists;
+DROP FOREIGN TABLE IF EXISTS test_rel_exists;
+
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+DROP TABLE test_rel_exists;
+DROP VIEW test_rel_exists;
+
+CREATE INDEX test_rel_exists ON test_if_exists_first.test_rel_with_index (ai);
+DROP TABLE test_rel_exists;
+DROP INDEX test_rel_exists;
+
+CREATE SEQUENCE test_rel_exists;
+DROP TABLE test_rel_exists;
+DROP SEQUENCE test_rel_exists;
+
+CREATE MATERIALIZED VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::bigint AS d, 'e'::text AS e;
+DROP TABLE test_rel_exists;
+
+DROP TABLE test_if_exists_second.test_rel_exists;
+DROP MATERIALIZED VIEW test_rel_exists;
+DROP TABLE test_if_exists_first.test_rel_with_index;
+
+-- Type & Domain behavior is thus:
+-- If Exists Behavior
+DROP DOMAIN IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_rel_exists;
+
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+DROP DOMAIN IF EXISTS test_rel_exists;
+CREATE DOMAIN test_rel_exists int4;
+DROP TABLE test_rel_exists;
+DROP DOMAIN test_rel_exists;
+
+-- Test with domain first and type second; plus table tests
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text);
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text); -- type with same name exists as table creation creates a composite type
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4; -- domain creation with same name as table fails as auto-generated type conflicts
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists; -- cannot independently drop a composite type associated with a table
+DROP TABLE test_if_exists_second.test_rel_exists;
+
+CREATE TYPE test_if_exists_second.test_rel_exists AS (c int, d text);
+CREATE TABLE test_if_exists_second.test_rel_exists (a int, b text); -- auto-created type prevents table from being created
+DROP TABLE test_if_exists_second.test_rel_exists; -- a standalone composite type cannot be dropped using the drop table command
+
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+CREATE DOMAIN test_rel_exists int4;
+DROP TYPE IF EXISTS test_rel_exists; -- DROP TYPE Drops the Domain
+DROP DOMAIN IF EXISTS test_if_exists_second.test_rel_exists;
+DROP DOMAIN test_rel_exists; -- double-checking the domain doesn't exist
+DROP TYPE test_rel_exists;
+
+-- Test with domain second and type first
+CREATE TYPE test_if_exists_first.test_rel_exists AS (c int, d text);
+CREATE DOMAIN test_if_exists_second.test_rel_exists int4;
+DROP DOMAIN IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_rel_exists;
+DROP TYPE IF EXISTS test_if_exists_second.test_rel_exists;
+
+DROP DOMAIN IF EXISTS test_rel_exists;
+-- /Type & Domain
+
+-- Bug # 16492 - this script produces an error, arguably it should not
+CREATE TABLE test_if_exists_first.test_rel_exists (a int, b text);
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP TABLE IF EXISTS test_if_exists_first.test_rel_exists;
+DROP VIEW IF EXISTS test_if_exists_first.test_rel_exists;
+CREATE VIEW test_if_exists_first.test_rel_exists AS
+    SELECT 1::int AS a, 'one'::text AS b;
+DROP VIEW test_if_exists_first.test_rel_exists;
+-- /Bug # 16492
+
 -- This test checks both the functionality of 'if exists' and the syntax
 -- of the drop database command.
 drop database test_database_exists (force);