I have noticed that in some instances if you update a row in mysql via the mysql_db module and the actual row data does not change - affected_rows will return 0. This is the default behaviour for the mysql API as per - http://dev.mysql.com/doc/refman/5.0/en/mysql-real-connect.html

There is a flag (CLIENT_FOUND_ROWS) that can be used in the mysql_real_connect function that will cause affected_rows to return the number of rows that were "matched" - ie in the WHERE clause, as opposed to whether or not any data was changed.

If we don't it could be a problem for modules like usrloc where an update is done and if no row are "affected" and new row is added which would cause a duplicate.

I understand that updating a row with zero changes is not ideal and prob. not a typical use case but this IMO is irrelevant. I understand affected rows to mean the number of rows that were matched and not the number of rows that had data changed... - seems like a case of MySQL being too clever here ;)

Thoughts? 

Cheers

Jason