Question

我有一张表格，表格如下

GROUP_ID | FOO | BAR | DATETIME

我有一个cron，每晚更新这张桌子。但是，我希望在我的脚本结束时运行一个sql命令，该命令将确保每个group_id的50个最新行都存在，而其他任何行都被删除。

例如：如果有60行且GROUP_ID = 1，我希望此次运行后只剩下最近的50行。如果GROUP_ID = 2只有20行，则将它们全部保留。

这只能在SQL中实现，还是我需要在PHP中实现这一点（我的大多数应用程序都是用它构建的）

我正在运行MySQL

由于

Answer 1

尝试使用此尺寸：

DELIMITER $$
DECLARE groupCursor CURSOR FOR
SELECT GROUP_ID FROM mytable WHERE 
(SELECT COUNT(*) FROM mytable WHERE GROUP_ID=GROUP_ID) > 50;

DECLARE CONTINUE HANDLER FOR NOT FOUND done = 1;

DECLARE groupID INT;

read_loop: LOOP
FETCH groupCursor INTO groupID;
IF done THEN
   LEAVE read_loop;
ELSE
   DELETE FROM mytable
   WHERE GROUP_ID = groupID
   AND DATETIME < (SELECT MIN(DATETIME) FROM mytable WHERE GROUP_ID=groupID 
   ORDER BY DATETIME DESC LIMIT 50)
END IF;
END LOOP;
CLOSE groupCursor$$
DELIMITER ;

UPDATE 根据下面的讨论，这是一个存储过程CREATE脚本，应该没有语法错误。

-- --------------------------------------------------------------------------------
-- Routine DDL
-- --------------------------------------------------------------------------------
DELIMITER $$

CREATE PROCEDURE `mydb`.`maintenanceTaskDelete` ()
BEGIN

DECLARE groupCursor CURSOR FOR SELECT GROUP_ID FROM mytable;
DECLARE done BIT DEFAULT 0;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

DECLARE groupID INT;

read_loop: LOOP
FETCH groupCursor INTO groupID;
IF done THEN
   LEAVE read_loop;
ELSE
   DELETE FROM mytable
   WHERE GROUP_ID = groupID
   AND DATETIME < (SELECT MIN(DATETIME) FROM mytable WHERE GROUP_ID=groupID 
   ORDER BY DATETIME DESC LIMIT 50);
END IF;
END LOOP;
CLOSE groupCursor;

END$$

要调用例程，您需要做的就是： CALL maintenanceTaskDelete();

Answer 2

尝试：

delete from yourtable 
where PK in (select pk 
             from (select 
                       pk, 
                       row_number() over(partition by GROUP_ID order by GROUP_ID, activity_date) as RowNumber
                   from yourtable
                   ) dt
             where RowNumber>50
            )

编辑我刚看到这是针对mysql而不是ms sql。 mysql没有row_number（）。

SQL维护脚本

2 个答案: