mysql - 如何使用 MySQL 删除一列中所有重复的行？

Question

我有一个表，其中一列 title 中有重复的值，因此 title 列有多个具有相同值的行。

我想删除所有重复项，但标题相同。

我可以执行哪种查询来完成此操作？

  Title     Subject             Description               Created_at
Something  Somethingsubject    Somethingdescription       2016-04-13 16:37:10  
Something  Anothersubject      Anotherdescription         2016-04-11 16:37:10
Something  Thirdsubject        Thirdsubject               2016-04-14 16:37:10
NumberTwo  NumberTwoSubject    NumberTwoSubject           2016-04-12 16:37:10
NumberTwo  AnotherNumberTwo    AnotherNumberTwoDescripti  2016-04-15 16:37:10

我想删除所有重复项，只留下一个，最好是最旧的记录，这样唯一剩下的记录就是:

Title        Subject            Description            Created_at
Something  Anothersubject     Anotherdescription    2016-04-11 16:37:10
NumberTwo  NumberTwoSubject    NumberTwoSubject     2016-04-12 16:37:10

Answer 1

你可以做一个自连接DELETE:

DELETE t1
FROM mytable t1
JOIN (SELECT Title, MAX(Created_at) AS max_date
      FROM mytable
      GROUP BY Title) t2
ON t1.Title = t2.Title AND t1.Created_at < t2.max_date   

Demo here