problem with overloading the "coalesce" function

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problem with overloading the "coalesce" function

От:
Emil Rachovsky <zsevgymko@yahoo.com>
Дата:


 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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Re: [GENERAL] problem with overloading the "coalesce" function

От:
Richard Huxton <dev@archonet.com>
Дата:
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

Re: [GENERAL] problem with overloading the "coalesce" function

От:
Emil Rachovsky <zsevgymko@yahoo.com>
Дата:


--- Richard Huxton  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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Re: [GENERAL] problem with overloading the "coalesce" function

От:
Richard Huxton <dev@archonet.com>
Дата:
Emil Rachovsky wrote:
> 
> --- Richard Huxton  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

Re: [GENERAL] problem with overloading the "coalesce" function

От:
Tom Lane <tgl@sss.pgh.pa.us>
Дата:
Richard Huxton  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
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