How to make sure that all the connections during mutiple talbes query are correctly placed?Are there any simple principles? I always find extra data when query between a couple of tables.

what database are u targeting?
basically it depends on the isolation level that you have chosen.
And keep all the queries in transaction blocks

Do you mean that after you've built a JOIN, you seem to have unwanted rows in the result set (because they slipped through the join conditions)? If that is the case, you need to check the primary keys of all of the tables involved, and make sure that you use them (if possible) for your joins.

If you meant something else, can you give us a few hints ???

-PatP

I find sketching a box for each table in thq query, and connecting them with lines for each join condition, helps if I am getting confused. Particularly useful when trying to follow someone else's huge query.

Thanks all! I appreciate all your help.