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

我想在我的字段中使用唯一的IP地址。我该如何删除所有重复的条目？

由于

Answer 1

删除MySQL中的重复项有点棘手，因为在子选择中无法引用表的愚蠢限制。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

修改

实际上有办法绕过愚蠢的子选择限制。如果表被包装到子选择内的派生表中，则MySQL解析器不会注意到这一点，并且很乐意使用子选择删除：

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

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testdata并更改了一条记录以使尾随空格。

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有同样的东西的另一个名字。

UPDATE2：由于mysql似乎不允许在delete语句中使用selfjoins，因此解决方法是使用辅助表，其中包含您（不想）保留的记录的ID。

（@ahose_with_no_name的解决方案更短，但是这个尝试保持接近普通的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;

Answer 3

试试这个

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;

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删除mysql数据库中的重复ip地址条目

3 个答案: