On Wed, Feb 12, 2014 at 9:24 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > James Harper <james.har...@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 -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
