Why do multiple EXISTS break a query - sql

Question

I am attempting to include a new table with values that need to be checked and included in a stored procedure. Statement 1 is the existing table that needs to be checked against, while statement 2 is the new table to check against.
I currently have 2 EXISTS conditions that function independently and produce the results I am expecting. By this I mean if I comment out Statement 1, statement 2 works and vice versa. When I put them together the query doesn't complete, there is no error but it times out which is unexpected because each statement only takes a few seconds.
I understand there is likely a better way to do this but before I do, I would like to know why I cannot seem to do multiple exists statements like this? Are there not meant to be multiple EXISTS conditions in the WHERE clause?
SELECT *
FROM table1 S
WHERE
--Statement 1
EXISTS
(
SELECT 1
FROM table2 P WITH (NOLOCK)
INNER JOIN table3 SA ON SA.ID = P.ID
WHERE P.DATE = #Date AND P.OTHER_ID = S.ID
AND
(
SA.FILTER = ''
OR
(
SA.FILTER = 'bar'
AND
LOWER(S.OTHER) = 'foo'
)
)
)
OR
(
--Statement 2
EXISTS
(
SELECT 1
FROM table4 P WITH (NOLOCK)
INNER JOIN table5 SA ON SA.ID = P.ID
WHERE P.DATE = #Date
AND P.OTHER_ID = S.ID
AND LOWER(S.OTHER) = 'foo'
)
)
EDIT: I have included the query details. Table 1-5 represent different tables, there are no repeated tables.

Answer 1

Too long to comment.
Your query as written seems correct. The timeout will only be able to be troubleshot from the execution plan, but here are a few things that could be happening or that you could benefit from.
Parameter sniffing on #Date. Try hard-coding this value and see if you still get the same slowness
No covering index on P.OTHER_ID or P.DATE or P.ID or SA.ID which would cause a table scan for these predicates
Indexes for the above columns which aren't optimal (including too many columns, etc)
Your query being serial when it may benefit from parallelism.
Using the LOWER function on a database which doesn't have a case sensitive collation (most don't, though this function doesn't slow things down that much)
You have a bad query plan in cache. Try adding OPTION (RECOMPILE) at the bottom so you get a new query plan. This is also done when comparing the speed of two queries to ensure they aren't using cached plans, or one isn't when another is which would skew the results.
Since your query is timing out, try including the estimated execution plan and post it for us at past the plan

Answer 2

I found putting 2 EXISTS in the WHERE condition made the whole process take significantly longer. What I found fixed it was using UNION and keeping the EXISTS in separate queries. The final result looked like the following:
SELECT *
FROM table1 S
WHERE
--Statement 1
EXISTS
(
SELECT 1
FROM table2 P WITH (NOLOCK)
INNER JOIN table3 SA ON SA.ID = P.ID
WHERE P.DATE = #Date AND P.OTHER_ID = S.ID
AND
(
SA.FILTER = ''
OR
(
SA.FILTER = 'bar'
AND
LOWER(S.OTHER) = 'foo'
)
)
)
UNION
--Statement 2
SELECT *
FROM table1 S
WHERE
EXISTS
(
SELECT 1
FROM table4 P WITH (NOLOCK)
INNER JOIN table5 SA ON SA.ID = P.ID
WHERE P.DATE = #Date
AND P.OTHER_ID = S.ID
AND LOWER(S.OTHER) = 'foo'
)