Providing an alternative result when there is no result

Hello all,

Is there an easy and efficient way to return a boolean false for a
query that returns no result, and true for one that does return a
result?

Currently we select the result into a temp table.

SELECT INTO temp_table id FROM ... ;
IF temp_table IS NULL THEN
resp:= 'NO';
ELSE
resp:= 'YES';
END IF;

I'd like to combine this into one step like this:
SELECT
   CASE
     WHEN id is null THEN 'NO'::text
     ELSE 'YES'::text
   END
FROM ...;

But, this is not have SELECT's work, I suppose. The CASE is never
encountered when there is no result, so in the "NO" case, NULL is
returned.

Any hints/tips? Is our original solution okay, or is there something
we can do to improve things?

Thanks,

Joshua Berry