刪除值

Question

我有一個MySQL表，它看起來是這樣的：

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

我想刪除有兩個重複值inrespective行的列的他們在因此示例如下所示：

id_one  id_two 
1   2 
3   2 
5   4 

總共有超過1200萬行。任何想法，我應該如何做到這一點？ PHP或MySQL查詢將是首選。

Answer 1

我勸了2步的方法：

1. 讓id_one總是較小的值，也就是說，如果id_one大於id_two然後交換它們的值 - 考慮這樣的事情（從here拍攝）：

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

2. 移除重複描述here：

   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) 
   

   （我假設你會對持有1200萬個條目的表的主鍵。）

沒有測試過，所以請備份您的數據！

Answer 2

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，因爲在mysql中你不能引用被更新或刪除的表。 既然你想備份副本，無論如何，你可以使用，而不是在EXISTS子查詢：

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 
    ); 

Answer 3

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