SQL刪除基於多列的行

Question

我有一個包含設備標識，設備讀取類型和設備讀取日期的八列的表。這三個欄是這樣的： Example Table

我想什麼做的是刪除每一行鍼對DevReadType = XX和每一行與匹配設備號，但一個DevReadDate小於日當DevReadType =「XX 」。我一直無法找到這種複雜條件的例子。幫助將不勝感激！

Answer 1

如果我理解正確的話，我會建議沿着線的東西：

DELETE d 
FROM device d 
JOIN (
    SELECT DevNum, MAX(DevReadDate) maxDevReadDate 
    FROM device 
    WHERE devReadType = 'xx' 
    GROUP BY DevNum 
) b 
ON d.DevNum = b.DevNum AND (d.DevReadDate < b.maxDevReadDate OR d.devReadType = 'xx') 

Answer 2

delete from device 
    where DevNum = @devicenum 
    and DevReadType = 'XX' 
    and DevReadDate < @date 

您可以先運行選擇againsr設備表測試你的where子句：

select * 
from device 
    where DevNum = @devicenum 
    and DevReadType = 'XX' 
    and DevReadDate < @date