ChrisM@Work (10/1/2013)
This I reckon is the correct way to write your query:
select T2.COL1, T2.COL2, T1.COL1, T1.COL2, T1.COL3from T1
join T2
on T1.COL4 = T2.COL3
where T2.COL4 != 'data1'
and T1.COL1 is not NULL
and T1.COL5 is not NULL
and T1.COL6 = 'data2'
AND NOT EXISTS (SELECT 1 FROM T3
WHERE T3.COL1 = T2.COL1
AND T3.COL2 = T2.COL2
AND T3.COL3 = T1.COL1
AND T3.COL4 = T1.COL2)
Check the results against the SELECT part of your original.
So in this case, it will select from T1 and T2, only if not in T3 ?
What if you want to include non-matches against T3 ? Would you add to the WHERE clause ?
and T3.COL1 is NULL
and T3.COL2 is NULL
and T3.COL3 is NULL
and T3.COL4 is NULL