after a few tests the solution with the Left Outer Join (DavidBurrows) yields the best performance compared to NOT EXISTS...

SELECT t1.field1,t1.field2,t1.field3 FROM Table1 t1 LEFT OUTER JOIN Table2 t2 ON...

NPeeters,

you are right the only way is to make a temp table (with the criteria)

and then JOIN the 2 tables. your solution is working.

Thanks

bill

UNION dont work because the number of combinations is not just 2 (perc=30 and numberoftests =2 AND perc=40 and numberoftests =1) but any combination for example

(perc=30 and numberoftests...