Question

我有四列，所有列都是varchar(x)。

DealerId
姓
名字
的StreetAddress

然后我有一个int列自动递增，名为SystemId。

我想要做的是删除我的表中4列匹配的所有行，但我想留下具有最大自动增量id的行。

例如

SystemId|DealerId|FirstName|LastName|StreetAddress
1|Hello|Mike|Tola|1923 somewhere dr
2|Hello|Mike|Tola|1923 somewhere dr

在上面的例子中，我想删除SystemId 1并离开SystemId 2。我有大约300k行，所以一个接一个地抓住这些id是不可能的。

Answer 1

您可以使用直接加入：

delete t2
from mytable t
join mytable t2 on t.dealerid = t2.dealerid
  and t.firstname = t2.firstname
  and t.lastname = t2.lastname
  and t.streetaddress = t2.streetaddress
  and t.systemid > t2.systemid

请参阅SQL Fiddle

技巧是t.systemid > t2.systemid的比较，它保持最高（最后添加）id。

Answer 2

您可以使用join：

执行此操作

delete t
    from table t join
         (select t2.dealerid, t2.firstname, t2.lastname, t2.streetaddress,
                 max(t2.systemId) as maxsystemid
          from table t2
          group by t2.dealerid, t2.firstname, t2.lastname, t2.streetaddress
         ) t2
         on t.dealerid = t2.dealerid and t.firstname = t2.firstname and
            t.lastname = t2.lastname and t.streetaddress = t2.streetaddress and
            t.systemid < t2.maxsystemid;

Answer 3

这应该有效

delete from table_name
where SystemId IN
(select t1.SystemId from table_name t1, table_name t2 where t1.DealerId=t2.DealerId and t1.firstname=t2.firstname and t1.lastname=t2.lastname and t1.streetaddress=t2.streetaddress and t1<t2  )

Answer 4

以下是使用最大SystemId

的连接的另一种方法

DELETE t
FROM mytable t
LEFT JOIN 
(
SELECT MAX(SystemId) SystemId
  FROM mytable
 GROUP BY DealerId,FirstName,LastName,StreetAddress

) t2
ON(t.SystemId = t2.SystemId)
WHERE t2.SystemId IS NULL

如何在保留至少一行的同时删除重复的MySQL表行

4 个答案:

Demo