At 12:07 -0400 7/3/02, Paul Tomsic wrote: >Does MySQL prevent updates from occurring when the values involved >are the same as the database's current state.
I don't know if "prevent" is the word exactly. It doesn't bother to update the row unless you actually change a value. The phenonenon you're observing is that the row-count value means "rows actually changed from their current values" rather than "rows select to be updated". > >For instance, if I've got a table > >create table updater( >id int not null primary key auto_increment, >is_active int not null default 1 >}; > >insert into updater(is_active) values (1); >insert into updater(is_active) values (1); > >update updater set is_active = 1; > >Would MySQL essentially disregard this update statement b/c the >values contained within the table are already 1? >Now, I realize that the values wouldn't be altered, but does the dB >do pre-checking and see which (if any) rows would be affected by the >query, and only run the update against rows that would be changed? > >There seems to be some reporting that is displayed which indicates >that MySQL DOES indeed to "pre-checking" > >mysql> select * from updater; >+----+-----------+ >| id | is_active | >+----+-----------+ >| 1 | 1 | >| 2 | 1 | >+----+-----------+ >2 rows in set (0.00 sec) > >mysql> update updater set is_active = 1; >Query OK, 0 rows affected (0.00 sec) >Rows matched: 2 Changed: 0 Warnings: 0 > >mysql> > >any thoughts? > >thanks, >Paul --------------------------------------------------------------------- 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
