如何使用MySQL删除一列中包含重复项的所有行？

Question

我有一个表在一列中有重复值,标题,因此标题列有多个具有相同值的行.

我想删除除标题相同之外的所有重复项.

我可以执行什么样的查询来完成此任务？

  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,以便剩下的唯一记录是:

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

你可以做一个自我加入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   

在这里演示