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  FROM  WHERE  = $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...