删除除最近 100 行以外的所有行

Question

我正在使用 MS SQL 数据库，我有一个名为 "Logs" 的 table，如下所示：

一条条记录在这里添加，所以 table 变得相当大 days/weeks。

我需要定期做的是一些清理工作。 IE。我需要一个 SQL 查询，该查询将删除旧行并仅保留此 table.

中最近的 100 条记录

我同意最好有它"delete records older than some_date"...以前是这样的，但是客户想要不同的:(所以...我们到了。

顺便说一句：我对人们对这个问题持否定态度感到有点失望。有什么不对吗？... 想象一下：这个问题已经产生了4个答案！ ... 一个人决定对此表示否定！现在我真的不知道怎么想了...这附近的陌生人:(

Answer 1

虽然我同意其他人的意见，这可能不是要走的路，但这里有一个方法可以做到：

;WITH keepers AS
(   SELECT TOP 100 [DateTime]
    FROM dbo.Logs
    ORDER BY [DateTime] DESC )
DELETE FROM dbo.Logs a
WHERE NOT EXISTS ( SELECT 1 FROM keepers b WHERE b.[DateTime] = a.[DateTime] )

Answer 2

您可以使用以下之一：

-- offset clause
WITH goners AS (
    SELECT *
    FROM Logs
    ORDER BY DateTime DESC
    OFFSET 100 ROWS 
)
DELETE FROM goners

-- numbered rows
WITH goners AS (
    SELECT ROW_NUMBER() OVER(ORDER BY DateTime DESC) AS rn, Logs.*
    FROM Logs
)
DELETE FROM goners
WHERE rn > 100

-- nth value
-- note that this "keeps" all rows that tie for last place
DELETE FROM Logs
WHERE DateTime < (
    SELECT MIN(DateTime)
    FROM (
        SELECT TOP 100 DateTime
        FROM Logs
        ORDER BY DateTime DESC
    ) AS x
)

Answer 3

不要使用 NOT EXISTS，只需使用 >=:

WITH keepers AS (
    SELECT TOP 100 [DateTime]
    FROM dbo.Logs
    ORDER BY [DateTime] DESC
   )
DELETE FROM dbo.Logs a
    WHERE l.DateTime < (SELECT MIN([DateTime]) FROM keepers);

我不确定 delete 是运行时是否有可以添加新行的锁定设置。如果是这样，这仍然是安全的。

您实际上可以在 SQL Server 2012+ 中简化此操作：

DELETE FROM dbo.Logs a
    WHERE l.DateTime < (SELECT [DateTime] 
                        FROM dbo.logs
                        ORDER BY [DateTime]
                        OFFSET 99 FETCH FIRST 1 ROW ONLY
                       );

Answer 4

DECLARE @cutoff DATETIME
SELECT TOP 100 @cutoff = [DateTime] FROM Logs ORDER BY [DateTime] DESC
DELETE FROM Logs WHERE [DateTime] < @cutoff

Answer 5

这对我有用：

;with cte as(select top(select count(*) - 100 from table) * from table order by dt)
delete from cte

删除除最近 100 行以外的所有行

Delete all rows except 100 most recent ones

sql

tsql

sql-server

datetime

sql-delete