SQL 刪除重復數據

有時候我們在使用sql數據庫的時候，想去掉重復數據，怎么去掉呢，下面來分享一下方法

我們在這里使用的數據庫是 mysql

創建表

首先我們創建一個  student 表

DROP TABLE IF EXISTS `student`;
CREATE TABLE `student`  (
  `id` int(0) NOT NULL,
  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `age` int(0) NULL DEFAULT NULL,
  `agx` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

插入數據

INSERT INTO `student` VALUES (1, '哈哈', 19, '男');
INSERT INTO `student` VALUES (2, '哈哈', 19, '女');
INSERT INTO `student` VALUES (3, '哈哈', 56, '女');
INSERT INTO `student` VALUES (4, '哈哈哈哈', 63, '男');

 

 使用sql找出需要保留的數據

我們保留 name 和 age 重復的數據（id 值最小的）

SELECT min(id),name,age FROM `student` GROUP BY `name`,age

 

 刪除重復的數據

DELETE FROM student WHERE id NOT IN (SELECT min_id FROM (SELECT min(id) as min_id FROM `student` GROUP BY `name`,age) as a)

 

 

 

 注：

如果使用 

DELETE FROM student WHERE id NOT IN (SELECT min(id) as min_id FROM `student` GROUP BY `name`,age)

在語法上看是沒問題的，但是在 MySQL中會出先 1093 - You can't specify target table 'student' for update in FROM clause  錯誤，但是在 mssql與oracle都沒有這個問題。