mysql 中删除重复字段数据的方式

1、创建一张表

CREATE TABLE `user` (
  `id` int(11) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `address` varchar(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

2、插入对应数据

INSERT INTO `user` VALUES ('1', 'zhangsan', '20', '上海');
INSERT INTO `user` VALUES ('2', 'zhangsan', '20', '北京');
INSERT INTO `user` VALUES ('3', 'lisi', '25', '北京');
INSERT INTO `user` VALUES ('4', 'lisi', '25', '深圳');
INSERT INTO `user` VALUES ('5', 'wangwu', '30', '深圳');
INSERT INTO `user` VALUES ('6', 'wangwu', '30', '上海');
INSERT INTO `user` VALUES ('7', 'zhaoliu', '35', '广州');

3、常用操作

#复制一张表
CREATE TABLE `user` as SELECT * FROM `user_temp`
#创建一张空表
CREATE TABLE user_temp1 like `user`
#删除一张表
DROP TABLE `user`

4、使用借助count关键字

DELETE FROM `user` WHERE id in(
    SELECT v.minid FROM(
            SELECT COUNT(*) num,`name`,age,MAX(id) minid FROM `user` GROUP BY `name`,age 
    ) v WHERE v.num>1
)

5、使用having关键字

DELETE FROM `user` WHERE id in(
    SELECT id FROM(
        SELECT MAX(id) id,`name`,age,address FROM `user` t GROUP BY t.`name` HAVING COUNT(`name`)>1
    ) v
)

注意：delete语句直接删除一条查询结果集是行不通的，必须借助内嵌视图也就是字查询来完成删除功能