MySQL删除重复数据

测试数据(一)

/* 表结构 */

DROP TABLE IF EXISTS `bas_info`;

CREATE TABLE IF NOT EXISTS `bas_info`(

`id` INT(1) NOT NULL AUTO_INCREMENT,

`chi_chi_name` VARCHAR(20) NOT NULL,

`trd_code` VARCHAR(20) NOT NULL,

PRIMARY KEY(`id`)

)Engine=InnoDB;

/* 插入测试数据 */

INSERT INTO `bas_info`(`id`,`chi_chi_name`,`trd_code`) VALUES

('1001','MSCI中华除B股+HSBC(红利总指)',"MSG033"),

('1002','MSCI中华除B股外(红利总指)',"MSG032"),

('1001','MSCI中华+HSBC(红利总指)',"MSG030"),

('1004','MSCI中华(红利总指)',"MSG031"),

('1005','MSCI中国民企股(红利总指)',"MSG031"),;

SELECT * FROM `bas_info`;

/* 查找id最小的重复数据(只查找id字段) */

SELECT DISTINCT MIN(`id`) AS `id`

FROM `bas_info`

GROUP BY `id`,`chi_chi_name`,`trd_code`

HAVING COUNT(1) > 1;

/* 查找所有重复数据 */

SELECT `bas_info`.*

FROM `bas_info`,(

SELECT `id`,`chi_chi_name`,`trd_code`

FROM `bas_info`

GROUP BY `id`,`chi_chi_name`,`trd_code`

HAVING COUNT(1) > 1

) AS `bas_info_test`

WHERE `bas_info`.`chi_name` = `bas_info_test`.`chi_name`

AND `bas_info`.`trd_code` = `bas_info_test`.`trd_code`;

/* 查找除id最小的数据外的重复数据 */

SELECT `bas_info`.*

FROM `bas_info`,(

SELECT DISTINCT MIN(`id`) AS `id`,`chi_name`,`trd_code`

FROM `bas_info`

GROUP BY `chi_name`,`trd_code`

HAVING COUNT(1) > 1001

) AS `bas_info_test`

WHERE `bas_info`.`chi_name` = `bas_info_test`.`chi_name`

AND `bas_info`.`trd_code` = `bas_info_test`.`trd_code`

AND `bas_info`.`id` <> `bas_info_test`.`id`;

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)

测试数据（二）

/* 表结构 */

DROP TABLE IF EXISTS `base_code`;

CREATE TABLE IF NOT EXISTS `base_code`(

`id` VARCHAR(20) NOT NULL COMMENT '字符串主键',

`chi_name` VARCHAR(20) NOT NULL,

`trd_code` VARCHAR(20) NOT NULL,

PRIMARY KEY(`id`)

)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 `base_code`(`id`,`chi_name`,`trd_code`) VALUES

('61001','中证香港',"L01141"),

('61002','中证香港',"L01141"),

('61003','中证香港',"L01141"),

/* 为表添加自增长的id字段 */

ALTER TABLE `base_code` trd_code `id` INT(1) NOT NULL AUTO_INCREMENT, trd_code INDEX `id`(`id`);

Query OK, 23 rows affected (0.16 sec)

Records: 23 Duplicates: 0 Warnings: 0

MySQL中必须是有索引的字段才可以使用AUTO_INCREMENT

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 */

DELETE FROM `base_code`

USING `base_code`,(

SELECT DISTINCT MIN(`id`) AS `id`,`chi_name`,`trd_code`

FROM `base_code`

GROUP BY `chi_name`,`trd_code`

HAVING COUNT(1) >61001

) AS `bas_info_test`

WHERE `base_code`.`chi_name` = `bas_info_test`.`chi_name`

AND `base_code`.`trd_code` = `bas_info_test`.`trd_code`

AND `base_code`.`id` <> `bas_info_test`.`id`;

Query OK, 2 rows affected (0.05 sec)

/* 删除id字段 */

ALTER TABLE `base_code` DROP `id`;

Query OK, 3 rows affected (0.16 sec)

Records: 3 Duplicates: 0 Warnings: 0