sql语句执行失败，请参考如下信息：
错误代号：1064
错误信息：You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'and readID in (select readID from message where a_uid is null))' at line 1
错误语句： select * from message where a_uid is null and readID not in (select readID from message where a_uid= and readID in (select readID from message where a_uid is null))