Обсуждение: problem with overloading the "coalesce" function

 Hi,
I am trying to overload the "coalesce" function to
accept an integer and a string. Here it is :

CREATE OR REPLACE FUNCTION "coalesce"(a int4, b
"varchar")
  RETURNS "varchar" AS
$BODY$
begin
 if (a is null ) then
   return b;
 else
  return cast(a as varchar(15));
end if;
end
$BODY$
  LANGUAGE 'plpgsql' VOLATILE;
ALTER FUNCTION "coalesce"(a int4, b "varchar") OWNER
TO postgres;

I have added it to pg_catalog, but still I cant't use
it, I get an error on the second parameter, apparently
the function gets lost at some point. Any additional
steps I need to complete?

Thanks in advance,
Emil

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Emil Rachovsky wrote:
>
>  Hi,
> I am trying to overload the "coalesce" function to
> accept an integer and a string. Here it is :
>
> CREATE OR REPLACE FUNCTION "coalesce"(a int4, b
> "varchar")
>   RETURNS "varchar" AS
...
> I have added it to pg_catalog, but still I cant't use
> it, I get an error on the second parameter

What is the error?

--
   Richard Huxton
   Archonet Ltd

--- Richard Huxton <dev@archonet.com> wrote:

> Emil Rachovsky wrote:
> >
> >  Hi,
> > I am trying to overload the "coalesce" function to
> > accept an integer and a string. Here it is :
> >
> > CREATE OR REPLACE FUNCTION "coalesce"(a int4, b
> > "varchar")
> >   RETURNS "varchar" AS
> ...
> > I have added it to pg_catalog, but still I cant't
> use
> > it, I get an error on the second parameter
>
> What is the error?

The error is :  invalid input syntax for integer
That is,it expects an integer as a second parameter,
since the first is an integer.


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Emil Rachovsky wrote:
>
> --- Richard Huxton <dev@archonet.com> wrote:
>
>> Emil Rachovsky wrote:
>>>  Hi,
>>> I am trying to overload the "coalesce" function to
>>> accept an integer and a string. Here it is :
>>>
>>> CREATE OR REPLACE FUNCTION "coalesce"(a int4, b
>>> "varchar")
>>>   RETURNS "varchar" AS
>> ...
>>> I have added it to pg_catalog, but still I cant't
>> use
>>> it, I get an error on the second parameter
>> What is the error?
>
> The error is :  invalid input syntax for integer
> That is,it expects an integer as a second parameter,
> since the first is an integer.

Hmm - looking at the source (and \df in psql) it seems the basic problem
is that COALESCE() isn't a function. It has its own code in the parser
and its own expression-node. So - your function never gets called
because the parser sees coalesce() and doesn't build a function - it
builds a coalesce-expression.

It should work fine if you rename your function of course.

HTH
--
   Richard Huxton
   Archonet Ltd

Richard Huxton <dev@archonet.com> writes:
> Hmm - looking at the source (and \df in psql) it seems the basic problem
> is that COALESCE() isn't a function.

If it were an ordinary function, it couldn't satisfy the property of not
evaluating "unused" arguments ...

            regards, tom lane