找到重复的mysql记录，并用最后一个重复值更新第一个副本 [英] Find duplicate mysql record and update first duplicate with last duplicate value

问题描述

我有一张这样的表。

ID    Name     Tag    
1     Orange   tea     
2     Pear     light    
3     Apple    tea
4     Juice    tea
5     Cocoa    baseball
6     Camera   baseball

我想做的是对于具有重复标签的行，我想更新第一次发生的名称与LATEST发生。

What I want to do is for rows that have duplicate TAGS, I want to update the name of FIRST occurence with the LATEST occurence.

所以在上面的例子中，我想将ID 1的名称从Orange更新为Juice，并删除其他（＃3，＃4）
并将ID 5从Cocoa更新为Camera并删除＃6。

So in example above, I would like to update ID 1's name from Orange to Juice and delete the others (#3,#4) And update ID 5 from Cocoa to Camera and delete #6.

如何使用PHP与PHP进行交互？或者可能只是在MySQL内部执行？

How would I do that using MySQL with PHP? Or maybe possible to just do it inside MySQL?

谢谢！

推荐答案

p>对于 UPDATE 查询，我们需要为每个标签获取最小和最大ID，只有有重复的行：

For the UPDATE query, we need to get the min and max ID's for each tag, only if there are duplicate rows:

UPDATE table t
  JOIN (
    SELECT MinID, b.Name LatestName
    FROM table b
    JOIN (
      SELECT MIN(ID) MinID, MAX(ID) MaxID
      FROM table
      GROUP BY tag
      HAVING COUNT(*) > 1
    ) g ON b.ID = g.MaxID
  ) rs ON t.ID = rs.MinID
SET t.Name = LatestName;

对于 DELETE 查询，我们全部删除不属于其标签组的第一个ID的行：

For the DELETE query, we delete all rows that are not the first ID's of its tag group:

DELETE t.*
FROM table t
  LEFT JOIN (
    SELECT MIN(ID) MinID
    FROM table
    GROUP BY tag
  ) g ON t.ID = g.MinID
WHERE g.MinID IS NULL;

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