Run explain select * from A,B where A.col1=B.col1;
The explain plan for your query will tell you what indexes are chosen. If your explain plan says what you do not like, definitely add an index on col1 in B. Make sure you run OPTIMIZE TABLE on both tables. The, run explain select * from A,B where A.col1=B.col1; again See what the explain plan says afterwards. Give it a try !!! ----- Original Message ----- From: "John Mancuso" <[EMAIL PROTECTED]> To: mysql@lists.mysql.com Sent: Thursday, June 21, 2007 10:07:39 AM (GMT-0500) America/New_York Subject: index question If I have 2 large tables A and B and I need to join them: select * from A,B where A.col1=B.col1 If A.col1 is an index and B.col1 is not, if I create an index on B.col1 will this index be used? In other words how are indexes used on table joins? Thanks John Mancuso Linux Administrator/MySQL DBA IT Infrastructure American Home Mortgage w: 631-622-6382 c: 516-652-2475 -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
