Quickest query to check for the existence of a row in Oracle?

Question

I\'m using Oracle, and I have a very large table. I need to check for the existence of any row meeting some simple criteria. What\'s the best way to go about this using simple

Answer 1

SELECT  NULL
FROM    x
WHERE   x.col_a = value_a
        AND x.col_b = value_b
        AND rownum = 1

COUNT(*) is certainly not the best way since it will need to count all the rows, while ROWNUM = 1 returns as soon as it finds the first matching row.

Here's the PL/SQL code:

DECLARE
        ex INT;
BEGIN
        BEGIN
                SELECT  NULL
                INTO    ex
                FROM    dual
                WHERE   1 = 1
                        AND rownum = 1;
                DBMS_OUTPUT.put_line('found');
        EXCEPTION
        WHEN no_data_found THEN
                DBMS_OUTPUT.put_line('not found');
        END;
END;