* [EMAIL PROTECTED] > 1 reason and 1 reason only. To speed up queries.
I would say there are three reasons to use indexes: 1) To speed up queries 2) To create constraints 3) To maintain a sort order If you have an order table and an order_line table, it is important that line no 1 only exists once for each order. order table: order_no customer_id order_date order_line table: order_no line_no product_id qty For the order_line table, an unique index[1] on (order_no,line_no) will make sure there is only one line no 1 for each order. It will also speed up queries involving order_line, and also make sure the sort order of the lines are correct, normally without the need of explicitly specifying ORDER BY. [1] This could be the primary key, or just a 'normal' unique index. -- Roger sql --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
