Query trouble - EXISTS doesnt work like I thought

Question

EXISTS is not behaving like I had hoped.
Help would be much appreciated
SELECT count(*) from OPPS
WHERE OPP_CODE = "A"
AND
EXISTS (
SELECT * FROM OPP_SUB_TABLE S, OPPS O
WHERE S.ID = O.ID AND
S.DTYPE = "1" AND S.DSUBTYPE = "2"
There are 14000 rows in OPPS where OPP_CODE="A"
There are only 31 rows in OPP_SUB_TABLE that have
both DTYPE = "1" and DSUBTYPE = "2"
I thought exists would work like an IN sort of, bringing me only 31 results.
Instead I get all 14000, what I am missing here?

Answer 1

EXISTS is like a boolean operation. It will return the row in your outer query if at least one row exists in your subquery.
Because you haven't coordinated the subquery with your outer query, every row will be returned (apparently because your inner query always returns a row).
I'm guessing you meant something like this:
SELECT count(*)
FROM   OPPS O
WHERE  O.OPP_CODE = 'A'
AND    EXISTS (SELECT 1
               FROM   OPP_SUB_TABLE S
               WHERE  S.ID = O.ID
               AND    S.DTYPE = '1'
               AND    S.DSUBTYPE = '2'
;(fixed the double quotes per Warren's example)
Message was edited by:
Eric H