php - 删除具有两个重复值的值，无论它们位于哪一列

Question

我有一个 mysql 表，它看起来像这样：

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，而不管它们在哪些列中，因此示例如下所示：

id_one     id_two
1          2
3          2
5          4

总共有超过 1200 万行。关于我应该如何做到这一点的任何想法？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 演示

Answer 2

我建议采用两步法：

1. 使 id_one 总是较小的值，即，如果 id_one 大于 id_two 则交换它们的值 - 考虑这样的事情（取自此处）：

   UPDATE tablename
   SET id_one = (@temp:=id_one), id_one = id_two, id_two = @temp
   WHERE id_one > id_two
   

2. 按照此处所述删除重复项：

   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)
   

   （我假设您将在包含 1200 万个条目的表上拥有一个主键。）

未测试，所以请备份您的数据！

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
    )
    ;

在 mysql 中不起作用，因为在 mysql 中您无法引用正在更新或删除的表。由于您无论如何都想制作备份副本，因此您可以在 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
   );