Help. Mysql Query optimisation not very clever?

Attention all Sql gurus, Is there a way to FORCE mysql resolve specific conditions within a query before wasting it's time trying to resolve other conditions? I THINK mssql is behaving foolishly in the way it goes about resolving the following situation. Tables : BN_SupMast : Reference table joined by SupCode field \ / | | BN_StkMast : Master table with 20,000 records | | / \ BN_StkLevl : Exactly 2 records per BN_StkMast table; Joined by StkCode When I execute a query explicitly specifying BN_StkMast key, it works perfectly as expected. EXAMPLE OF QUERY THAT WORKS FINE : $Q = "select * from BN_StkLevl as sl, BN_StkMast as sm, BN_SupMast as sup where" only dif.---> ." sm.StkCode='0005'"

                ." and sl.StkCode=sm.StkCode"
                ." and sm.StkSupplierUsual=sup.SupCode"

If, instead, I execute a query with a more vague condition on the BN_StkMast table, the entire system hangs. I'm guessing this is because mySql is first resolving the condition that links all the BN_SupMast records against all the BN_StkMast records? I can't think why else it would hang. EXAMPLE OF QUERY THAT HANGS: $Q = "select * from BN_StkLevl as sl, BN_StkMast as sm, BN_SupMast as sup where" only dif.---> ." sm.StkDescription like 'age%'"

                ." and sl.StkCode=sm.StkCode"
                ." and sm.StkSupplierUsual=sup.SupCode"

In case you are thinking that this query might just return truck-loads of results, this is not the case. If I REMOVE the BN_StkLevl table from the above queries, then both work fine (also, if I remove BN_SupMast they both work fine). It must be MySql somehow doing something odd. Sorry for being so long-winded, but can any one help? Thanks ... Ross

. Ross Honniball                  JCU Bookshop Cairns Supervisor

. James Cook Uni, McGreggor Rd, Smithfield, Qld. 4878, Australia . Ph:07.4042.1157 Fx:07.4042.1158 Em:ross@bookshop.jcu.edu.au . There are no problems. Only solutions.