What is the difference in IN (select..) and exists? Whe does the first query return nothing but the second one does?
Thanks

-- tblclaimheader.ilsid and tbllocation.ilsid are both int(4)

select * from tblclaimheader ch
where ch.ilsid not in (select l.ilsid from tbllocation L)
-- returns no records
select * from tblclaimheader ch where ch.ilsid = 1 and
ch.ilsid not in (select l.ilsid from tbllocation L where l.ilsid = 1)
-- returns 1 record

select ch.* from tblclaimheader ch where not exists (select * from tbllocation L where l.ilsid = ch.ilsid)
-- returns 1841 records
select * from tblclaimheader where ilsid = 1
-- returns 1 record
select * from tbllocation where ilsid = 1
-- returns no records