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 SQL?

Here’s my best guess, and while it may turn out to be fast enough for my purposes, I’d love to learn a canonical way to basically do SQL Server’s “exists” in Oracle:

select count(x_id) from x where x.col_a = value_a and x.col_b = value_b;

The count() would then be returned as a boolean in another tier. The main point is that I want Oracle to do the bare minimum for this query – I only need to know if there are any rows matching the criteria.

And yes, those columns will most definitely be indexed.

Answer 1

Using COUNT(*) is OK if you also use rownum=1:

declare
   l_cnt integer;
begin
   select count(*)
   into   l_cnt
   from   x
   where  x.col_a = value_a 
   and    x.col_b = value_b
   and    rownum = 1;
end;

This will always return a row, so no need to handle any NO_DATA_FOUND exception. The value of l_cnt will be 0 (no rows) or 1 (at least 1 row exists).