Обсуждение: overloaded functions and NULL

I thought all ambiguous function calls would generate an error:

ERROR:  function g("unknown") is not unique
HINT:  Could not choose a best candidate function. You may need to add
explicit type casts.

but this doesn't seem to be the case.  The below code creates overloaded
functions that do not produce this error when called with a NULL argument.

jurka=# CREATE FUNCTION g(int) RETURNS int AS 'SELECT 1;' LANGUAGE sql;
CREATE FUNCTION
jurka=# CREATE FUNCTION g(float) RETURNS int AS 'SELECT 2;' LANGUAGE sql;
CREATE FUNCTION
jurka=# SELECT g(NULL);
 g
---
 2
(1 row)


Kris Jurka

Kris Jurka <books@ejurka.com> writes:
> The below code creates overloaded
> functions that do not produce this error when called with a NULL argument.

> jurka=# CREATE FUNCTION g(int) RETURNS int AS 'SELECT 1;' LANGUAGE sql;
> CREATE FUNCTION
> jurka=# CREATE FUNCTION g(float) RETURNS int AS 'SELECT 2;' LANGUAGE sql;
> CREATE FUNCTION

float (a/k/a float8) is the preferred type in the numeric hierarchy,
so it will win in a tug-of-war against int.  There are other cases
where it would lose (eg, had you declared g(text)).  The objective
of the type rules is most certainly not to fail in any ambiguous
situation --- if we did, we'd have a completely unusable system.

            regards, tom lane

Tom Lane wrote:
 > Kris Jurka <books@ejurka.com> writes:
 >
 >>The below code creates overloaded
 >>functions that do not produce this error when called with a NULL argument.
 >
 >
 >>jurka=# CREATE FUNCTION g(int) RETURNS int AS 'SELECT 1;' LANGUAGE sql;
 >>CREATE FUNCTION
 >>jurka=# CREATE FUNCTION g(float) RETURNS int AS 'SELECT 2;' LANGUAGE sql;
 >>CREATE FUNCTION
 >
 >
 > float (a/k/a float8) is the preferred type in the numeric hierarchy,
 > so it will win in a tug-of-war against int.  There are other cases
 > where it would lose (eg, had you declared g(text)).  The objective
 > of the type rules is most certainly not to fail in any ambiguous
 > situation --- if we did, we'd have a completely unusable system.

I have to had that in normal cases the g argument type is a known type
so all is automagically solved:


CREATE OR REPLACE FUNCTION sp_bar ( INTEGER )
RETURNS INTEGER AS'
BEGIN
   RAISE NOTICE ''INTEGER'';
   return 0;
END;
' LANGUAGE 'plpgsql';


CREATE OR REPLACE FUNCTION sp_bar ( FLOAT )
RETURNS INTEGER AS'
BEGIN
   RAISE NOTICE ''FLOAT'';
   return 0;
END;
' LANGUAGE 'plpgsql';


CREATE OR REPLACE FUNCTION sp_foo (  )
RETURNS INTEGER AS'
DECLARE
   my   INTEGER := 4;
BEGIN
   perform sp_bar( my );
   my = NULL;
   perform sp_bar( my );

   return 0;
END;
' LANGUAGE 'plpgsql';



# select sp_foo();
NOTICE:  INTEGER
CONTEXT:  PL/pgSQL function "sp_foo" line 4 at perform
NOTICE:  INTEGER
CONTEXT:  PL/pgSQL function "sp_foo" line 6 at perform
  sp_foo
--------
       0
(1 row)




AS the OP can see even calling sp_bar with a null value then
the correct function is called.



Regards
Gaetano Mendola