您确定您执行的最后一个查询是INSERT吗？
mysqli->insert_id似乎是正确的答案：
Return Values
The value of the
AUTO_INCREMENTfield that was updated
by the prevIoUs query. Returns zero if
there was no prevIoUs query on the
connection or if the query did not
update anAUTO_INCREMENTvalue.
