Re: Boolean SQL function ?

Bo Lorentsen <bl(at)netgroup(dot)dk> writes:
> How does one write a SQL FUNCTION that works in a WHERE clause ?
> If fx. I like to make a function called "is_today" that take two dates
> and test if they are within the same day, how can I express this in SQL
> ?

Something like this:

test71=# create function same_day(timestamp, timestamp) returns bool as
test71-# 'select $1::date = $2::date' language 'sql';
CREATE
test71=# select same_day(now(), 'today'::timestamp);
same_day
----------
t
(1 row)

test71=# select same_day(now(), 'yesterday'::timestamp);
same_day
----------
f
(1 row)

test71=#

This particular example doesn't need to use any boolean constants,
but when you do, you can write them like so:
true
false
't'::bool
'f'::bool

regards, tom lane