Re: polymorphic SQL functions has a problem with domains

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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