mysql去除重复记录案例
2024-09-02 23:57:26
例1，表中有主键(可唯一标识的字段)，且该字段为数字类型
1 测试数据
/* 表结构 */
DROP TABLE IF EXISTS `t1`;
CREATE TABLE IF NOT EXISTS `t1`(
`id` INT(1) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(20) NOT NULL,
`add` VARCHAR(20) NOT NULL,
PRIMARY KEY(`id`)
)Engine=InnoDB; /* 插入测试数据 */
INSERT INTO `t1`(`name`,`add`) VALUES
('abc',"123"),
('abc',"123"),
('abc',"321"),
('abc',"123"),
('xzy',"123"),
('xzy',"456"),
('xzy',"456"),
('xzy',"456"),
('xzy',"789"),
('xzy',"987"),
('xzy',"789"),
('ijk',"147"),
('ijk',"147"),
('ijk',"852"),
('opq',"852"),
('opq',"963"),
('opq',"741"),
('tpk',"741"),
('tpk',"963"),
('tpk',"963"),
('wer',"546"),
('wer',"546"),
('once',"546"); SELECT * FROM `t1`;
+----+------+-----+
| id | name | add |
+----+------+-----+
| 1 | abc | 123 |
| 2 | abc | 123 |
| 3 | abc | 321 |
| 4 | abc | 123 |
| 5 | xzy | 123 |
| 6 | xzy | 456 |
| 7 | xzy | 456 |
| 8 | xzy | 456 |
| 9 | xzy | 789 |
| 10 | xzy | 987 |
| 11 | xzy | 789 |
| 12 | ijk | 147 |
| 13 | ijk | 147 |
| 14 | ijk | 852 |
| 15 | opq | 852 |
| 16 | opq | 963 |
| 17 | opq | 741 |
| 18 | tpk | 741 |
| 19 | tpk | 963 |
| 20 | tpk | 963 |
| 21 | wer | 546 |
| 22 | wer | 546 |
| 23 | once | 546 |
+----+------+-----+
rows in set (0.00 sec)
2 查找id最小的重复数据(只查找id字段)
/* 查找id最小的重复数据(只查找id字段) */ SELECT DISTINCT
MIN(`id`) AS `id`
FROM
t1
GROUP BY
`name`,
`add`
HAVING
COUNT(1) > 1; +------+
| id |
+------+
| 1 |
| 12 |
| 19 |
| 21 |
| 6 |
| 9 |
+------+
rows in set (0.00 sec)
3 查找所有重复数据
SELECT `t1`.*
FROM `t1`,(
SELECT `name`,`add`
FROM `t1`
GROUP BY `name`,`add`
HAVING COUNT(1) > 1
) AS `t2`
WHERE `t1`.`name` = `t2`.`name`
AND `t1`.`add` = `t2`.`add`; +----+------+-----+
| id | name | add |
+----+------+-----+
| 1 | abc | 123 |
| 2 | abc | 123 |
| 4 | abc | 123 |
| 6 | xzy | 456 |
| 7 | xzy | 456 |
| 8 | xzy | 456 |
| 9 | xzy | 789 |
| 11 | xzy | 789 |
| 12 | ijk | 147 |
| 13 | ijk | 147 |
| 19 | tpk | 963 |
| 20 | tpk | 963 |
| 21 | wer | 546 |
| 22 | wer | 546 |
+----+------+-----+
rows in set (0.00 sec)
4 查找除id最小的数据外的重复数据
SELECT `t1`.*
FROM `t1`,(
SELECT DISTINCT MIN(`id`) AS `id`,`name`,`add`
FROM `t1`
GROUP BY `name`,`add`
HAVING COUNT(1) > 1
) AS `t2`
WHERE `t1`.`name` = `t2`.`name`
AND `t1`.`add` = `t2`.`add`
AND `t1`.`id` <> `t2`.`id`;
+----+------+-----+
| id | name | add |
+----+------+-----+
| 2 | abc | 123 |
| 4 | abc | 123 |
| 7 | xzy | 456 |
| 8 | xzy | 456 |
| 11 | xzy | 789 |
| 13 | ijk | 147 |
| 20 | tpk | 963 |
| 22 | wer | 546 |
+----+------+-----+
rows in set (0.00 sec)
5 删除重复数据，只保留一条数据 id最小的
DELETE FROM t1 USING t1,
(
SELECT
DISTINCT MIN(`id`) AS `id`,`name`,`add`
FROM t1
GROUP BY `name`, `add`
HAVING COUNT(1) > 1
) AS t2 //选中重复记录id最小的
WHERE
t1.`name` = t2.`name`
AND t1.`add` = t2.`add`
AND t1.id <> t2.id; 受影响的行: 8
时间: 0.111s
6 查看数据库 SELECT
t1.id,
t1.`name`,
t1.`add`
FROM
t1 1 abc 123
3 abc 321
5 xzy 123
6 xzy 456
9 xzy 789
10 xzy 987
12 ijk 147
14 ijk 852
15 opq 852
16 opq 963
17 opq 741
18 tpk 741
19 tpk 963
21 wer 546
23 once 546
例2，表中没有主键(可唯一标识的字段)，或者主键并非数字类型(也可以删除重复数据，但效率上肯定比较慢)
1 测试数据 /* 表结构 */
DROP TABLE IF EXISTS `noid`;
CREATE TABLE IF NOT EXISTS `noid`(
`pk` VARCHAR(20) NOT NULL COMMENT '字符串主键',
`name` VARCHAR(20) NOT NULL,
`add` VARCHAR(20) NOT NULL,
PRIMARY KEY(`pk`)
)Engine=InnoDB; /* 测试数据，与上例一样的测试数据，只是主键变为字符串形式 */
INSERT INTO `noid`(`pk`,`name`,`add`) VALUES
('a','abc',"123"),
('b','abc',"123"),
('c','abc',"321"),
('d','abc',"123"),
('e','xzy',"123"),
('f','xzy',"456"),
('g','xzy',"456"),
('h','xzy',"456"),
('i','xzy',"789"),
('j','xzy',"987"),
('k','xzy',"789"),
('l','ijk',"147"),
('m','ijk',"147"),
('n','ijk',"852"),
('o','opq',"852"),
('p','opq',"963"),
('q','opq',"741"),
('r','tpk',"741"),
('s','tpk',"963"),
('t','tpk',"963"),
('u','wer',"546"),
('v','wer',"546"),
('w','once',"546"); SELECT * FROM `noid`;
+----+------+-----+
| pk | name | add |
+----+------+-----+
| a | abc | 123 |
| b | abc | 123 |
| c | abc | 321 |
| d | abc | 123 |
| e | xzy | 123 |
| f | xzy | 456 |
| g | xzy | 456 |
| h | xzy | 456 |
| i | xzy | 789 |
| j | xzy | 987 |
| k | xzy | 789 |
| l | ijk | 147 |
| m | ijk | 147 |
| n | ijk | 852 |
| o | opq | 852 |
| p | opq | 963 |
| q | opq | 741 |
| r | tpk | 741 |
| s | tpk | 963 |
| t | tpk | 963 |
| u | wer | 546 |
| v | wer | 546 |
| w | once | 546 |
+----+------+-----+
rows in set (0.00 sec)
2 为表添加自增长的id字段
/* 为表添加自增长的id字段 */
ALTER TABLE `noid` ADD `id` INT(1) NOT NULL AUTO_INCREMENT, ADD INDEX `id`(`id`);
Query OK, 23 rows affected (0.16 sec)
Records: 23 Duplicates: 0 Warnings: 0 SELECT * FROM `noid`;
+----+------+-----+----+
| pk | name | add | id |
+----+------+-----+----+
| a | abc | 123 | 1 |
| b | abc | 123 | 2 |
| c | abc | 321 | 3 |
| d | abc | 123 | 4 |
| e | xzy | 123 | 5 |
| f | xzy | 456 | 6 |
| g | xzy | 456 | 7 |
| h | xzy | 456 | 8 |
| i | xzy | 789 | 9 |
| j | xzy | 987 | 10 |
| k | xzy | 789 | 11 |
| l | ijk | 147 | 12 |
| m | ijk | 147 | 13 |
| n | ijk | 852 | 14 |
| o | opq | 852 | 15 |
| p | opq | 963 | 16 |
| q | opq | 741 | 17 |
| r | tpk | 741 | 18 |
| s | tpk | 963 | 19 |
| t | tpk | 963 | 20 |
| u | wer | 546 | 21 |
| v | wer | 546 | 22 |
| w | once | 546 | 23 |
+----+------+-----+----+
rows in set (0.00 sec)
MySQL中必须是有索引的字段才可以使用AUTO_INCREMENT
3 删除重复数据与上例一样，记得删除完数据把id字段也删除了
删除重复数据，只保留一条数据 保留id最小的
DELETE FROM `noid`
USING `noid`,(
SELECT DISTINCT MIN(`id`) AS `id`,`name`,`add`
FROM `noid`
GROUP BY `name`,`add`
HAVING COUNT(1) > 1
) AS `t2`
WHERE `noid`.`name` = `t2`.`name`
AND `noid`.`add` = `t2`.`add`
AND `noid`.`id` <> `t2`.`id`;
Query OK, 8 rows affected (0.05 sec)
= 删除id字段 =
ALTER TABLE `noid` DROP `id`;
Query OK, 15 rows affected (0.16 sec)
Records: 15 Duplicates: 0 Warnings: 0 SELECT * FROM `noid`;
+----+------+-----+
| pk | name | add |
+----+------+-----+
| a | abc | 123 |
| c | abc | 321 |
| e | xzy | 123 |
| f | xzy | 456 |
| i | xzy | 789 |
| j | xzy | 987 |
| l | ijk | 147 |
| n | ijk | 852 |
| o | opq | 852 |
| p | opq | 963 |
| q | opq | 741 |
| r | tpk | 741 |
| s | tpk | 963 |
| u | wer | 546 |
| w | once | 546 |
+----+------+-----+
rows in set (0.00 sec)
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