有两张表bas_student、bas_householder,
去除学生表中与家长表重复的手机号
UPDATE bas_student a,bas_householder b SET a.mobile=NULL WHERE a.mobile=b.HouseHolderMobile AND LENGTH(a.Mobile)=11;
mysql多表条件更新
原文：http://www.cnblogs.com/xbblogs/p/7412782.html
