function with different return type depending on parameter?

Hey
http://www.postgresql.org/docs/9.3/static/plpgsql-declarations.html
at anyelement.

Cheers
Rémi-C

2014-02-12 10:20 GMT+01:00 James Harper <james.harper@bendigoit.com.au>:

Hello

no it is not possible

Regards

Pavel

p.s. result - type must be known before execution (when execution plan is
created)

2014-02-12 10:20 GMT+01:00 James Harper <james.harper@bendigoit.com.au>:

James Harper <james.harper@bendigoit.com.au> writes:

is it possible to have a function that can return a different type
depending on the parameters?

The data type of any expression (including a function call) has to be
determinable at parse time, so no you can't just randomly return a
run-time-determined data type.

However, have you looked at the "polymorphic functions" feature?
You can declare a function as returning the same data type that
one of its inputs has. This seems to cover most of the cases
that are useful in practice.

http://www.postgresql.org/docs/9.3/static/extend-type-system.html#EXTEND-TYPES-POLYMORPHIC
http://www.postgresql.org/docs/9.3/static/xfunc-sql.html#AEN52916

regards, tom lane

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On Wed, Feb 12, 2014 at 9:24 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

James Harper <james.harper@bendigoit.com.au> writes:

is it possible to have a function that can return a different type
depending on the parameters?

The data type of any expression (including a function call) has to be
determinable at parse time, so no you can't just randomly return a
run-time-determined data type.

However, have you looked at the "polymorphic functions" feature?
You can declare a function as returning the same data type that
one of its inputs has. This seems to cover most of the cases
that are useful in practice.

http://www.postgresql.org/docs/9.3/static/extend-type-system.html#EXTEND-TYPES-POLYMORPHIC
http://www.postgresql.org/docs/9.3/static/xfunc-sql.html#AEN52916

You can also define a function to return 'text', which by virtue of
every other type being able to be casted to/from text, can be used as
a kind of variant. This technique is pretty dubious mostly, but can
occasionally be used to work around problematic situations.

There's also hstore for dealing with record-variant situations (this
is especially useful in, say, auditing triggers), and it's emerging
strong contender: json. All of the text variant approaches though
simply defer the type resolution to some later point, which can lead
to performance and logical consistency issues if you're not careful.

merlin

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