在mysql5中,可以设置safe mode,比如在一个更新语句中
UPDATE table_name SET bDeleted=0;
执行时会错误,报:
You are using safe update mode and you tried to update a table without a WHERE clause that uses a KEY column.”
  原因是在safe mode下,要强制安全点,update只能跟where了,
要取消这个限制,可以:
    SET SQL_SAFE_UPDATES=0;
即可