MySQL怎样删除重复数据，只保留一条？

在实际工作开发过程中，常常会遇到数据库表中存在多条数据重复了，此时我们需要删除重复数据，只保留其中一条有效的数据；

针对这种场景，我们用SQL语句该怎么实现呢？

数据准备

建表语句：

DROP TABLE IF EXISTS `test`;CREATE TABLE `test`  (  `id` int(11) NULL DEFAULT NULL,  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;INSERT INTO `test` VALUES (1, '张三');INSERT INTO `test` VALUES (2, '李四');INSERT INTO `test` VALUES (4, '张三');INSERT INTO `test` VALUES (5, '王二');INSERT INTO `test` VALUES (6, '护具');INSERT INTO `test` VALUES (7, '无极');INSERT INTO `test` VALUES (8, '护具');INSERT INTO `test` VALUES (3, '空气');INSERT INTO `test` VALUES (9, '王二');INSERT INTO `test` VALUES (10, '几乎');commit;

查看重复数据，并筛选

select t.name,count(1) from test t where 1=1 group by t.name ;

使用having语句进行筛选

select t.name,count(1) from test t where 1=1 group by t.name HAVING count(1) >1;

对于重复数据，保留一条数据筛选

select t.name,min(id) as  id ,count(1) from test t where 1=1 group by t.name;

删除重复数据

delete from test where id not in (select  min(id)  from test t where 1=1 group by t.name ) ;

执行上述SQL语句，发现会报错：

delete from test where id not in (select  min(id)  from test t where 1=1 group by t.name )> 1093 - You can't specify target table 'test' for update in FROM clause> 时间: 0.004s

导致这一原因的问题是：不能在同一表中查询的数据作为同一表的更新数据。

正确参考SQL:

(1) 创建一张表temp_table存储最终保留的数据。create table temp_table as SELECT min( id ) as id FROM test t WHERE 1 = 1 GROUP BY t.NAME;(2) 排除表temp_table中的数据，删除即可。DELETE FROM test WHERE id NOT IN (SELECT * FROM temp_table);

成功删除重复数据！