Обсуждение: 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

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

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