Unique constraints and indexes.
Is this a bug? I create a "unique" index, directly but it doesn't add a unique
constraint. Add a unique constraint and it adds the index and the constraint.
(pg version 9.4.5 on fedora 22, but also occurs in other versions).
Functionally I can't see a difference.
mydb=# create table test_table ( f1 bigint, f2 bigint);
CREATE TABLE
mydb=# create unique index test_table_un on test_table (f1, f2);
CREATE INDEX
mydb=# \d test_table
Table "public.test_table"
Column | Type | Modifiers
--------+--------+-----------
f1 | bigint |
f2 | bigint |
Indexes:
"test_table_un" UNIQUE, btree (f1, f2)
mydb=# select conindid, contype, conname from pg_constraint where conname like
'test_table%';
conindid | contype | conname
----------+---------+---------
(0 rows)
-- --------------------------------------------------------------------------
mydb=# drop table test_table;
DROP TABLE
mydb=# create table test_table ( f1 bigint, f2 bigint);
CREATE TABLE
mydb=# alter table test_table add constraint test_table_un unique (f1,f2);
ALTER TABLE
mydb=# \d test_table
Table "public.test_table"
Column | Type | Modifiers
--------+--------+-----------
f1 | bigint |
f2 | bigint |
Indexes:
"test_table_un" UNIQUE CONSTRAINT, btree (f1, f2)
mydb=# select conindid, contype, conname from pg_constraint where conname like
'test_table%';
conindid | contype | conname
----------+---------+---------------
4284073 | u | test_table_un
(1 row)
mydb=#
--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general
Steve Rogerson <steve.pg@yewtc.demon.co.uk> writes:
Is this a bug? I create a "unique" index, directly but it doesn't add a unique
constraint. Add a unique constraint and it adds the index and the constraint.
That's operating as designed. A unique constraint needs an index,
but not vice versa.
regards, tom lane
--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general
On 05/01/16 19:47, Tom Lane wrote:
Steve Rogerson <steve.pg@yewtc.demon.co.uk> writes:
Is this a bug? I create a "unique" index, directly but it doesn't add a unique
constraint. Add a unique constraint and it adds the index and the constraint.That's operating as designed. A unique constraint needs an index,
but not vice versa.
I can see that might be plausible , hence the question but as a "unique index"
imposes as constraint they seem equivalent. What's the functional difference
between the two situations?
Steve
--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general
On Tuesday, January 5, 2016, Steve Rogerson <steve.pg@yewtc.demon.co.uk>
wrote:
On 05/01/16 19:47, Tom Lane wrote:
Steve Rogerson <steve.pg@yewtc.demon.co.uk <javascript:;>> writes:
Is this a bug? I create a "unique" index, directly but it doesn't add a
unique
constraint. Add a unique constraint and it adds the index and the
constraint.
That's operating as designed. A unique constraint needs an index,
but not vice versa.I can see that might be plausible , hence the question but as a "unique
index"
imposes as constraint they seem equivalent. What's the functional
difference
between the two situations?
I suspect it has to do with partial unique indexes.
David J.
Steve Rogerson <steve.pg@yewtc.demon.co.uk> writes:
On 05/01/16 19:47, Tom Lane wrote:
That's operating as designed. A unique constraint needs an index,
but not vice versa.
I can see that might be plausible , hence the question but as a "unique index"
imposes as constraint they seem equivalent. What's the functional difference
between the two situations?
There is none so far as uniqueness-enforcement is concerned, because the
index is the same either way, and that's what enforces it.
The main reason we don't automatically create a constraint for every
unique index is that not all index declarations can be represented
by SQL-standard constraints.
regards, tom lane
--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general