Question

示例table_1

ID Email         Answer   UpdateDate
1  xxx.@xx.com   1        2011-07-02
2  xxx.@xx.com   3        2011-07-11
3  vvv.@xx.com   3        2011-07-12
4  vvv.@xx.com   5        2011-07-13
5  xxx.@xx.com   5        2011-07-14
6  xxx.@xx.com   4        2011-07-14
7  xxx.@xx.com   4        2011-07-14
8  zzz.@xx.com   4        2011-07-15

如何删除此记录，但保留最新的UpdateDate

结果：

ID Email         Answer   UpdateDate
4  vvv.@xx.com   5        2011-07-13
7  xxx.@xx.com   4        2011-07-14
8  zzz.@xx.com   4        2011-07-15

Answer 1

我会根据相关的子查询检查UpdateDate。

CREATE TEMPORARY TABLE
  latestRecord (
    Email        VARCHAR(128),
    updateDate   DATETIME
) 
INSERT INTO 
  latestRecord
SELECT
  Email,
  MAX(updateDate) AS updateDate
FROM
  table_1
GROUP BY
  Emal

DELETE 
  table_1
FROM
  table_1
INNER JOIN
  latestRecord
    ON  latestRecord.Email      = table_1.Email
    AND latestRecord.updateDate < table_1.updateDate

修改

同一逻辑的另一个重构

Answer 2

确保UpdateDate是DATETIME字段。

您是否希望为每个答案值保留最新的UpdateDate？这样就可以了：

delete from table_1 where UpdateDate not in ( select max(UpdateDate) from table_1 group by Answer );

如果您只想保留最新日期：

delete from table_1 where UpdateDate not in ( select max(UpdateDate) from table_1 );

Answer 3

您可以使用临时变量来存储最高日期，然后使用单独的查询来删除所有＆lt;比起那个来说。请记住，变量是特定于连接的。

select max(UpdateDate) from table_1 into @TempUpdateDate

delete from table_1 where UpdateDate < @TempUpdateDate

如何删除MySQL中的记录并保留最新日期

3 个答案: