mysql_affected_rows() returns the number of rows affected by the last INSERT, UPDATE or DELETE query associated with link_identifier. If the link identifier isn't specified, the last link opened by mysql_connect() is assumed.
Note: If you are using transactions, you need to call mysql_affected_rows() after your INSERT, UPDATE, or DELETE query, not after the commit.
If the last query was a DELETE query with no WHERE clause, all of the records will have been deleted from the table but this function will return zero.
Note: When using UPDATE, MySQL will not update columns where the new value is the same as the old value. This creates the possiblity that mysql_affected_rows() may not actually equal the number of rows matched, only the number of rows that were literally affected by the query.
mysql_affected_rows() does not work with SELECT statements; only on statements which modify records. To retrieve the number of rows returned by a SELECT, use mysql_num_rows().
If the last query failed, this function will return -1.
See also: mysql_num_rows().