MySQL删除重复数据-解决线上数据库存在重复数据的问题

目标：去掉同一字段下的重复数据或者仅仅留下一条

案例:

CREATE TABLE `student` (

  `id` INT(11) NOT NULL AUTO_INCREMENT,

  `name` VARCHAR(20) DEFAULT NULL,

  `age` INT(11) DEFAULT NULL,

  PRIMARY KEY (`id`)

) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

 

INSERT INTO `student` (`id`, `name`, `age`) VALUES ('1', 'cat', 22);

INSERT INTO `student` (`id`, `name`, `age`) VALUES ('2', 'dog', 33);

INSERT INTO `student` (`id`, `name`, `age`) VALUES ('3', 'fish', 44);

INSERT INTO `student` (`id`, `name`, `age`) VALUES ('4', 'cat', 55);

INSERT INTO `student` (`id`, `name`, `age`) VALUES ('5', 'dog', 11);

INSERT INTO `student` (`id`, `name`, `age`) VALUES ('6', 'cat', 45);



SELECT * FROM student;

如何编写查看有重复记录的SQL？

公式：

Select * From 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(1)>1)

案例：

SELECT * FROM student WHERE NAME IN (SELECT NAME FROM student GROUP BY NAME HAVING COUNT(1)>1)

如何编写删除重复记录的SQL?

1.重复的数据全部删除

DELETE FROM student WHERE NAME IN (
    SELECT t.NAME FROM ( SELECT NAME FROM student GROUP BY NAME HAVING COUNT( 1 ) > 1 ) t
)

2.重复的数据要求删除，仅保留一条

第一步

# 删除表中删除重复数据仅保留一条
# select看看
SELECT
 * 
FROM
 student 
WHERE
 id NOT IN (
   SELECT
   t.id 
   FROM
   ( SELECT MIN( id ) AS id FROM student GROUP BY `name` ) t 
 )

第二步

# delete搞定
DELETE
FROM
 student 
WHERE
 id NOT IN (  SELECT  t.id   FROM   ( SELECT MIN( id ) AS id FROM student GROUP BY `name` ) t  )