Do you know that if you create seq column on the original table as an auto_increment primary key, it will fill in the numbers automatically? There's no need to create the values on another table and update with a join.
Regards, Gavin Towey -----Original Message----- From: Hank [mailto:hes...@gmail.com] Sent: Wednesday, September 02, 2009 4:35 PM To: mysql@lists.mysql.com Subject: Speeding up a pretty simple correlated update query Hello All, I have a legacy application which was written using a compound primary key of an item number (non unique) along with a category ID. The combination of the item number and category ID make the records unique. I am in the process of replacing the compound (VARCHAR) keys with an unique integer key in these tables. So I have created an item_seq table and assigned a unique sequence number to each compound key -- it looks like this (all tables are myisam tables, and mysql version 5.0) desc item_seq; +-----------+------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------+------------------+------+-----+---------+----------------+ | seq | int(10) unsigned | NO | PRI | NULL | auto_increment | | itemid | char(11) | NO | MUL | | | | category | char(4) | NO | | | | +-----------+------------------+------+-----+---------+----------------+ I also have my main transactional table with about 180,000,000 rows -- it looks like this: desc item_trans; +-------------+-----------------------+------+-----+---------------------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------+-----------------------+------+-----+---------------------+-------+ | seq | int(10) unsigned | NO | MUL | | | | itemid | char(11) | NO | PRI | | | | category | char(4) | NO | PRI | | | | transid | int(10) | NO | PRI | | | Currently the "seq" field is null for the entire table. So of course, I want to update the main transaction table with the new sequence number. So I've disabled all the keys on the "item_trans" table -- since I am updating every row, it wouldn't (shouldn't) be using the index anyway. Here is my correlated update query: update item_trans i, item_seq is set i.seq=is.seq where is.itemid=i.itemid and is.category=i.category; If I run an explain on the select version of the update, this is what I get: +----+-------------+----------+--------+---------------+--------+---------+------------------------------------------------+-----------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------+--------+---------------+--------+---------+------------------------------------------------+-----------+-------+ | 1 | SIMPLE | item_trans | ALL | PRIMARY | NULL | NULL | NULL | 178948797 | | | 1 | SIMPLE | item_seq | eq_ref | itemid | itemid | 20 | g.item_trans.itemid,g.item_trans.category | 1 | | +----+-------------+----------+--------+---------------+--------+---------+------------------------------------------------+-----------+-------+ ... which is exactly what I would expect it to do. Update every record of the item_trans table, and do a full index lookup on the items_seq table. SO... I've been running this query to update item_trans, and it's been running for 5 days now. I've also tried running this with the primary key index on the item_trans table (but not the seq index), and that ran slower in my initial tests. Are there any faster ways to update 180 million records with a correlated update query? And I'm fairly certain that trying to do this in PHP one-record at a time would take much longer than a SQL solution. Thanks, -Hank The information contained in this transmission may contain privileged and confidential information. It is intended only for the use of the person(s) named above. If you are not the intended recipient, you are hereby notified that any review, dissemination, distribution or duplication of this communication is strictly prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
