FW: INSERT WHERE NOT EXISTS

// check if entry already exists
SELECT COUNT(*) FROM tablename WHERE [cond]
..
if($count >0)
UPDATE
else
INSERT

but this will double the hit to the database server, because
for every
operation I need to do SELECT COUNT(*) first. The data itself
is not a lot,
and the condition is not complex, but the hitting frequency is a lot.

Why not use plpgsql?

CREATE FUNCTION a_test(int4) RETURNS int AS '
DECLARE
totest int;
BEGIN
SELECT INTO totest <ID> FROM <table> WHERE <ID> = $1;

IF totest IS null THEN
-- do insert.
return 1;
ELSE
-- do update.
return 0;
END IF;
END;
' language 'plpgsql';

For efficiency make sure ID is a index...