mysql - 删除mysql数据库中重复的ip地址条目

Question

我的数据库中有重复的 IP 地址记录，如下所示：

id | ipaddress
1    192.168.xxx.xxx
2    192.168.xxx.xxx
3    111.118.xxx.xxx
4    111.118.xxx.xxx

我想在我的领域中使用唯一的 IP 地址。我应该如何删除所有重复的条目？

谢谢

Answer 1

由于无法在子选择中引用表的愚蠢限制，在 MySQL 中删除重复项有点棘手。因此需要将子选择重新写入连接：

DELETE d
FROM mytable d
LEFT JOIN (
   SELECT min(id) as min_id
   FROM   mytable
   GROUP BY trim(ipaddress)
) tokeep ON tokeep.min_id = d.id
WHERE keep.min_id IS NULL;

SQLFiddle 演示：http ://sqlfiddle.com/#!2/9cfb9c/1

编辑

实际上有一种方法可以绕过愚蠢的子选择限制。如果该表被包装到子选择中的派生表中，MySQL 解析器不会注意到这一点，并愉快地使用子选择删除：

delete mt 
from mytable mt
where exists (
    select * 
    from (
      select id, ipaddress
      from mytable
    ) ex
    where TRIM(ex.ipaddress) = TRIM(mt.ipaddress)
   and ex.id < mt.id
)

Answer 2

尝试这个

DELETE * FROM MyTable AS aa INNER JOIN (
  SELECT MIN(id) as MID, id, ipaddress FROM MyTable
  GROUP BY id, ipaddress HAVING COUNT(*) > 1
) AS bb ON bb.id = aa.id AND bb.ipaddress = aa.ipaddress
  AND bb.MID <> aa.id;

访问此链接

Answer 3

CREATE TABLE mytable
        (id SERIAL NOT NULL PRIMARY KEY
        , ipaddress varchar
        );
INSERT INTO mytable(id, ipaddress) VALUES
 (1, '192.168.xxx.xxx')
,(2, '192.168.xxx.xxx ')        --<< note trailing whitespace
,(3, '111.118.xxx.xxx')
,(4, '111.118.xxx.xxx')
        ;
SELECT * FROM mytable;

DELETE FROM mytable mt
WHERE EXISTS (
  SELECT * FROM mytable ex
  WHERE ex.ipaddress = mt.ipaddress
  AND ex.id < mt.id
  )
  ;
SELECT * FROM mytable;

DELETE FROM mytable mt
WHERE EXISTS (
  SELECT * FROM mytable ex
  WHERE TRIM(ex.ipaddress) = TRIM(mt.ipaddress)
  AND ex.id < mt.id
  )
  ;
SELECT * FROM mytable;

输出：

CREATE TABLE
INSERT 0 4
 id |    ipaddress     
----+------------------
  1 | 192.168.xxx.xxx
  2 | 192.168.xxx.xxx 
  3 | 111.118.xxx.xxx
  4 | 111.118.xxx.xxx
(4 rows)

DELETE 1
 id |    ipaddress     
----+------------------
  1 | 192.168.xxx.xxx
  2 | 192.168.xxx.xxx 
  3 | 111.118.xxx.xxx
(3 rows)

DELETE 1
 id |    ipaddress    
----+-----------------
  1 | 192.168.xxx.xxx
  3 | 111.118.xxx.xxx
(2 rows)

更新：添加了测试数据并将一条记录更改为具有尾随空格。

注意：字符串函数的名称可能因 DMBS 实现而异。TRIM() 函数适用于 postgres，也许 mysql 对同一事物有另一个名称。

UPDATE2：由于 mysql 似乎不允许在删除语句中使用 selfjoins，因此一种解决方法是使用带有您（不）想要保留的记录的 id 的辅助表。

（@ahose_with_no_name 的解决方案更短，但这个解决方案试图保持接近普通 SQL）：

CREATE table without_dups(id INTEGER NOT NULL);
INSERT INTO without_dups(id)
SELECT id
FROM mytable mt
WHERE NOT EXISTS (
  SELECT * FROM mytable ex
  WHERE ex.ipaddress = mt.ipaddress
  AND ex.id < mt.id
  )
  ;

DELETE FROM mytable mt
WHERE NOT EXISTS (
  SELECT * FROM without_dups nx
  WHERE nx.id = mt.id
  )
  ;

DROP TABLE without_dups;

SELECT * FROM mytable;