Question

我知道这听起来很混乱，但我不知道如何更好地解释它。我在下面简化了一个表格：

DB Type       ID
================
Table1         1                 
Table1         2                 
Table1         3                 
Table1         4                 
Table1         5                 
Table2         6                 
Table2         7                 
Table2         8                 
Table2         9                 
Table2        10

我想要实现的是基本上清理掉这个表但是如果有意义的话，保留每个数据库类型的最高ID的记录 - 所以在这种情况下它将是（表1,5）和（表2,10））删除所有其他记录。是否可以通过MySQL独占完成？

*的修改 ***

感谢Yogendra Singh的提示

DELETE FROM MyTable WHERE ID NOT IN (SELECT * FROM (SELECT MAX(ID) from MyTable GROUP BY DB Type) AS tb1 ) ORDER BY ID ASC

Answer 1

首先选择最ID组db_type，然后将其用作not in的子查询。

 DELETE FROM MyTable 
 WHERE ID NOT IN 
    (SELECT ID FROM 
      (SELECT MAX(ID) AS ID from MyTable GROUP BY DB Type) AS tb1
    )

编辑：

 DELETE FROM MyTable
 HAVING MAX(ID) > ID;

Answer 2

delete your_table
from
  your_table left join
  (select max(id) max_id from your_table group by type) mx
  on your_table.id=mx.max_id
where mx.max_id is null

子查询返回每种类型的最大ID，这些是要保留的值。使用左连接，我选择表中没有in_ max_ids的所有行，这些是要删除的行。这只有在id是主键时才有效，否则我们也必须加入类型。

Answer 3

组合数据库类型 - ID是唯一的吗？

如果是这样，你可以分两个阶段攻击它：

只获取您想要的行

SELECT [DB Type], Max(ID) AS MaxID
FROM YourTable
GROUP BY [DB Type]

删除其余部分（将前一个语句包含在更复杂的语句中;不代表）

DELETE FROM YourTable
FROM
    YourTable
    LEFT JOIN
    (SELECT [DB Type], Max(ID) AS MaxID
     FROM YourTable GROUP BY [DB Type]) DontDelete
    ON
      YourTable.[DB Type]=DontDelete.[DB Type] AND
      YourTable.ID=DontDelete.MaxID
WHERE
  DontDelete.[DB Type] IS NULL

Answer 4

DELETE FROM MyTable del
WHERE EXISTS ( 
    (SELECT * 
     FROM MyTable xx
     WHERE xx."db Type" = del."db Type"
     AND xx.id > del.id
     );

Answer 5

delete from my_Table  
 where Day in (select  MAX(day) d from my_Table   where id='id')

从表中删除记录＆lt;字段的最大数量并保持最高数字

5 个答案: