The mysql_insert_id() function returns the ID generated by a query on a table with a column having the AUTO_INCREMENT attribute or the value for the last usage of LAST_INSERT_ID(expr). If the last query wasn't an INSERT or UPDATE statement or if the modified table does not have a column with the AUTO_INCREMENT attribute and LAST_INSERT_ID was not used, this function will return zero.
When performing a multi-insert statement, mysql_insert_id() will return the value of the first row.
