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

I think using EXISTS gives a more natural answer to the question than trying to optimise a COUNT query using ROWNUM.

Let Oracle do the ROWNUM optimisation for you.

create or replace function is_exists (
        p_value_a varchar2,
        p_value_b varchar2)
        return boolean
is

   v_exists varchar2(1 char);

begin

    begin
        select 'Y' into v_exists from dual
        where exists
            (select 1 from x where x.col_a = p_value_a and x.col_b = p_value_a);

    exception

        when no_data_found then

            v_exists := null;

    end;

    return v_exists is not null;

end is_exists;