Question

我有一个mysql表，看起来像这样：

id_one     id_two
1          2
2          1
3          2
2          3
4          5
5          4

我想删除具有两个重复值的行，无论它们位于哪个列中，所以示例如下所示：

id_one     id_two
1          2
3          2
5          4

总共超过1200万行。关于我应该怎么做的任何想法？首选Php或mysql查询。

Answer 1

DELETE a
FROM table1 a
LEFT JOIN
    (
      select id_one, id_two
      from   Table1
      GROUP BY least(id_one, id_two), greatest(id_one, id_two)
    ) b ON a.id_one = b.id_one AND a.id_two = b.id_two
WHERE b.id_two IS NULL

SQLFiddle Demo

Answer 2

我建议采用两步法：

使id_one始终为较小的值，即如果id_one大于id_two，则交换它们的值 - 考虑这样的事情（取自here）：
```
UPDATE tablename
SET id_one = (@temp:=id_one), id_one = id_two, id_two = @temp
WHERE id_one > id_two
```

按照here：

所述删除重复项

DELETE tablename FROM tablename INNER JOIN
    (SELECT min(primary_key) AS min_id, id_one, id_two FROM tablename
     GROUP BY id_one, id_two
     HAVING count(1) > 1) AS d
ON (d.id_one = tablename.id_one
    AND d.id_two = tablename.id_two
    AND d.min_id <> tablename.primary_key)

（我假设您将拥有一个包含1200万个条目的表的主键。）

未经测试，请备份您的数据！

Answer 3

DELETE FROM ztable zt
WHERE zt.id_one > zt.id_two
  AND EXISTS (
    SELECT * 
    FROM ztable tx
    WHERE tx.id_one = zt.id_two
      AND tx.id_two = zt.id_one
    )
    ;

不能在mysql中工作，因为在mysql中你无法引用正在更新或删除的表。既然你想要制作备份副本，你可以在EXISTS子查询中使用它：

CREATE table safetable AS (SELECT * from ztable);

DELETE FROM ztable zt 
WHERE zt.id_one > zt.id_two 
AND EXISTS (
   SELECT * 
   FROM safetable tx
   WHERE tx.id_one = zt.id_two 
     AND tx.id_two = zt.id_one
   );

删除具有两个重复值的值，而不管它们位于哪个列中

3 个答案: