domains, case statements, functions: bug?

On 07/08/2013 10:26 AM, Joe Van Dyk wrote:

create domain m numeric(5,2);
create table t (c m);
create function f(t) returns m as $ select case when true then $1.c end
$ language sql;

psql:/tmp/t1.sql:3: ERROR: return type mismatch in function declared to
return m
DETAIL: Actual return type is numeric.
CONTEXT: SQL function "f"

Interesting:

test=> select case when true then t.c end from t;
case
-------
54.36
(1 row)

test=> create function f(t) returns m as $$ select case when true then
$1.c end $$ language sql;

ERROR: return type mismatch in function declared to return m

DETAIL: Actual return type is numeric.

CONTEXT: SQL function "f"

test=> create function f(t) returns numeric as $$ select case when true
then $1.c end $$ language sql;

CREATE FUNCTION

test=> select f(t);
ERROR: column "t" does not exist
LINE 1: select f(t);

I will admit I am at a loss. Maybe someone else can illuminate.

--
Adrian Klaver
adrian.klaver@gmail.com

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Adrian Klaver <adrian.klaver@gmail.com> writes:

test=> create function f(t) returns m as $$ select case when true then
$1.c end $$ language sql;
ERROR: return type mismatch in function declared to return m
DETAIL: Actual return type is numeric.

pg_typeof is somewhat helpful here:

regression=# select pg_typeof(t.c) from t;
pg_typeof
-----------
m
(1 row)

regression=# select pg_typeof(case when true then t.c end) from t;
pg_typeof
-----------
numeric
(1 row)

The reason for this is that CASE uses select_common_type() to infer the
output type, and select_common_type intentionally discriminates against
domain types. The comment therein says:

* If all input types are valid and exactly the same, just pick that type.
* This is the only way that we will resolve the result as being a domain
* type; otherwise domains are smashed to their base types for comparison.

So the way to get a CASE to return a domain type is to be sure you
provide an ELSE with the same result type:

regression=# select pg_typeof(case when true then t.c else null::m end) from t;
pg_typeof
-----------
m
(1 row)

regards, tom lane

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On 07/08/2013 06:58 PM, Tom Lane wrote:

Adrian Klaver <adrian.klaver@gmail.com> writes:

test=> create function f(t) returns m as $$ select case when true then
$1.c end $$ language sql;
ERROR: return type mismatch in function declared to return m
DETAIL: Actual return type is numeric.

pg_typeof is somewhat helpful here:

regression=# select pg_typeof(t.c) from t;
pg_typeof
-----------
m
(1 row)

regression=# select pg_typeof(case when true then t.c end) from t;
pg_typeof
-----------
numeric
(1 row)

The reason for this is that CASE uses select_common_type() to infer the
output type, and select_common_type intentionally discriminates against
domain types. The comment therein says:

* If all input types are valid and exactly the same, just pick that type.
* This is the only way that we will resolve the result as being a domain
* type; otherwise domains are smashed to their base types for comparison.

So the way to get a CASE to return a domain type is to be sure you
provide an ELSE with the same result type:

regression=# select pg_typeof(case when true then t.c else null::m end) from t;
pg_typeof
-----------
m
(1 row)

Found out something new, thanks.

So the following works:

test=> CREATE OR REPLACE FUNCTION utility.f(t)
RETURNS numeric
LANGUAGE sql
AS $function$ select case when true then $1.c else null::m end $function$
;
CREATE FUNCTION

regards, tom lane

--
Adrian Klaver
adrian.klaver@gmail.com

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