Обсуждение: polymorphic SQL functions has a problem with domains

Pavel Stehule <pavel.stehule@gmail.com> writes:
> I was informed about impossibility to use a polymorphic functions together
> with domain types

> see

>  create domain xx as numeric(15);

> create or replace function g(anyelement, anyelement)
> returns anyelement as
> $$  select $1 + $2 $$
> language sql immutable;

> postgres=# select g(1::xx, 2::xx);
> ERROR:  return type mismatch in function declared to return xx
> DETAIL:  Actual return type is numeric.
> CONTEXT:  SQL function "g" during inlining

That example doesn't say you can't use polymorphic functions with domains.
It says that this particular polymorphic function definition is wrong:
it is not making sure its result is of the expected data type.  I don't
recall right now whether SQL functions will apply an implicit cast on the
result for you, but even if they do, an upcast from numeric to some domain
over numeric wouldn't be implicit.
        regards, tom lane

Tom Lane-2 wrote
> Pavel Stehule <

> pavel.stehule@

> > writes:
>> I was informed about impossibility to use a polymorphic functions
>> together
>> with domain types
> 
>> see
> 
>>  create domain xx as numeric(15);
> 
>> create or replace function g(anyelement, anyelement)
>> returns anyelement as
>> $$  select $1 + $2 $$
>> language sql immutable;
> 
>> postgres=# select g(1::xx, 2::xx);
>> ERROR:  return type mismatch in function declared to return xx
>> DETAIL:  Actual return type is numeric.
>> CONTEXT:  SQL function "g" during inlining
> 
> That example doesn't say you can't use polymorphic functions with domains.
> It says that this particular polymorphic function definition is wrong:
> it is not making sure its result is of the expected data type.  I don't
> recall right now whether SQL functions will apply an implicit cast on the
> result for you, but even if they do, an upcast from numeric to some domain
> over numeric wouldn't be implicit.

How would that be possible though?  Since any number of domains could be
defined over numeric as soon as the "+" operator causes the domain to be
lost there is no way to get it back manually - you cannot just make it
"SELECT ($1 + $2)::xx".

Does something like:

SELECT ($1 + $2)::$1%TYPE 

exist where you can explicitly cast to the type of the input argument?

David J.




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David Johnston <polobo@yahoo.com> writes:
> Does something like:
> SELECT ($1 + $2)::$1%TYPE 
> exist where you can explicitly cast to the type of the input argument?

I don't think SQL-language functions have such a notation, but it's
possible in plpgsql, if memory serves.
        regards, tom lane

On 2014-04-02 12:27:30 -0400, Tom Lane wrote:
> David Johnston <polobo@yahoo.com> writes:
> > Does something like:
> > SELECT ($1 + $2)::$1%TYPE 
> > exist where you can explicitly cast to the type of the input argument?
> 
> I don't think SQL-language functions have such a notation, but it's
> possible in plpgsql, if memory serves.

Sometimes you can play nasty tricks using COALESCE() to force a cast
like that.
E.g. SELECT COALESCE(NULLIF($1, $1), $1 + $2);

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services

Tom Lane-2 wrote
> David Johnston <

> polobo@

> > writes:
>> Does something like:
>> SELECT ($1 + $2)::$1%TYPE 
>> exist where you can explicitly cast to the type of the input argument?
> 
> I don't think SQL-language functions have such a notation, but it's
> possible in plpgsql, if memory serves.

Indeed.

http://www.postgresql.org/docs/9.3/interactive/plpgsql-declarations.html#PLPGSQL-DECLARATION-TYPE

Section 40.3.3

You lose inlining but at least it (should) work.

David J.






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