How to generate a set of functions in PostgreSQL

Create   Function Join_two_with_comma ( Text , Text ) Returns   Text
Language SQL
As $ _ $
Select   Case
When $ 2   Is   Null   Or $ 2   =   ''   Then $ 1
When $ 1   Is   Null   Or $ 1   =   ''   Then $ 2
Else $ 1   |   ' , '   | $ 2
End
$ _ $;

Create aggregate join_with_comma ( text ) (
sfunc = join_two_with_comma,
stype = text ,< br> initcond = ''
);