Question

我开发了一个查询，根据字段清除除最近添加的行之外的所有行 - ＆gt;存储为文本的时间戳和用户ID字段。

还涉及更改日期格式，因此也涉及一些合并。

这是删除查询 - ＆gt;

DELETE
FROM `table` main
WHERE COALESCE(STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CDT %Y' ), STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CST %Y' )) <
  (SELECT  MAX(COALESCE(STR_To_DATE( sub.Timestamp , '%a %b %d %H:%i:%s CDT %Y' ), STR_To_DATE( sub.Timestamp , '%a %b %d %H:%i:%s CST %Y' ))) 
  FROM `table` sub
  WHERE sub.Retrieving_User = main.Retrieving_User )

这不会运行，抛出此错误 - ＆gt;

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'main WHERE COALESCE(STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CDT %Y' ),' at line 2

我明白这是什么，不知道为什么会这样。如果我将查询更改为选择 - > <>;

SELECT *
FROM `table` main
WHERE COALESCE(STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CDT %Y' ), STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CST %Y' )) <
  (SELECT  MAX(COALESCE(STR_To_DATE( sub.Timestamp , '%a %b %d %H:%i:%s CDT %Y' ), STR_To_DATE( sub.Timestamp , '%a %b %d %H:%i:%s CST %Y' ))) 
  FROM `table` sub
  WHERE sub.Retrieving_User = main.Retrieving_User )

它正确地抓取了我要删除的所有数据。

请告诉我，我不必更改查询的格式，因为我整个上午都花在了它上面。：（

编辑：

我通过研究发现，您无法从子查询中使用的同一个表中删除。所以我为此创建了一个很长的解决方法......稍后会更新......

Answer 1

DELETE from `table` where COALESCE(STR_To_DATE( Timestamp , '%a %b %d %H:%i:%s CDT %Y' ), STR_To_DATE( Timestamp , '%a %b %d %H:%i:%s CST %Y' )) in
(
SELECT COALESCE(STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CDT %Y' ), STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CST %Y' ))
FROM `table` main
WHERE COALESCE(STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CDT %Y' ), STR_To_DATE( main.Timestamp , '%a %b %d %H:%i:%s CST %Y' )) <
(SELECT  MAX(COALESCE(STR_To_DATE( sub.Timestamp , '%a %b %d %H:%i:%s CDT %Y' ), STR_To_DATE( sub.Timestamp , '%a %b %d %H:%i:%s CST %Y' ))) 
FROM `table` sub
WHERE sub.Retrieving_User = main.Retrieving_User)
)

选择查询工作，删除不？

1 个答案: