SELECT greatest(a,b) FROM bar
would return one tuple for every record in the table with a single value representing the greater of bar.a and bar.b.
You could define your own functions to do this but it would be tiresome to define one for every datatype.
In 7.4devel (just starting beta) you can do this:
create or replace function greatest(anyelement, anyelement) returns anyelement as 'select case when $1 > $2 then $1 else $2 end' language 'sql';
regression=# select greatest(1, 2);
greatest
----------
2
(1 row)regression=# select greatest('b'::text, 'a');
greatest
----------
b
(1 row)regression=# select greatest(now(), 'yesterday');
greatest
-------------------------------
2003-07-01 13:21:56.506106-07
(1 row)The cast to text is needed because 'a' and 'b' are really typed as unknown, and with polymorphic functions, you need a well defined data type.
So if you had a table:
create table g(f1 text, f2 text);
insert into g values ('a','b');
insert into g values ('c','b');
regression=# select greatest(f1, f2) from g;
greatest
----------
b
c
(2 rows)Doesn't help for 7.3.x, but at least you know help is on the way ;-) Of course, you could always just use the case statement.
Joe
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