场景：
有一个活动成员表，有活动Id和成员Id列，要求处理掉重复的成员，即同一活动下，去掉活动Id和成员Id重复的记录。
表结构：
-- ---------------------------- -- Table structure for `MEMBER` -- ---------------------------- DROP TABLE IF EXISTS `MEMBER`; CREATE TABLE `MEMBER` ( `ID` int(11) NOT NULL AUTO_INCREMENT, `ACTIVITY_ID` int(11) DEFAULT NULL, `USER_ID` int(11) DEFAULT NULL, PRIMARY KEY (`ID`), KEY `FK_Reference_32` (`ACTIVITY_ID`) USING BTREE, KEY `INDEX_ACTMEB_USER` (`USER_ID`) USING BTREE ) ENGINE=InnoDB AUTO_INCREMENT=1448271 DEFAULT CHARSET=utf8
插入数据：
-- ---------------------------- -- Records of MEMBER -- ---------------------------- INSERT INTO `MEMBER` VALUES (‘1‘, ‘1‘, ‘11001‘); INSERT INTO `MEMBER` VALUES (‘2‘, ‘1‘, ‘11001‘); INSERT INTO `MEMBER` VALUES (‘3‘, ‘1‘, ‘37001‘); INSERT INTO `MEMBER` VALUES (‘4‘, ‘2‘, ‘37002‘); INSERT INTO `MEMBER` VALUES (‘5‘, ‘2‘, ‘37002‘); INSERT INTO `MEMBER` VALUES (‘6‘, ‘1‘, ‘37001‘);
查找多余的重复数据：
SELECT m1.* FROM MEMBER m1,( SELECT ID,ACTIVITY_ID,USER_ID FROM MEMBER GROUP BY ACTIVITY_ID,USER_ID HAVING COUNT(1) > 1 ) AS m2 WHERE m1.ACTIVITY_ID = m2.ACTIVITY_ID AND m1.USER_ID = m2.USER_ID AND m1.ID <> m2.ID
删除多余的重复数据：
原文：http://www.cnblogs.com/google4y/p/3578075.html