如何刪除 MySQL 中的記錄並保留最新日期

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

如何刪除此記錄但保留最新的UpdateDate

結果：

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

我會根據相關的子查詢檢查 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

編輯

相同邏輯的另一個重構

Answer 2

確保 UpdateDate 是 DATETIME 字段。

您想為每個 Answer 值保留最新的 UpdateDate 嗎？ 這將做到這一點：

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，則：

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

Answer 3

您可以使用臨時變量來存儲最高日期，然后使用單獨的查詢來刪除 < 的所有內容。 請記住，變量是特定於連接的。

select max(UpdateDate) from table_1 into @TempUpdateDate

delete from table_1 where UpdateDate < @TempUpdateDate