SQL删除基于多列的行

Question

我有一个包含设备标识，设备读取类型和设备读取日期的八列的表。这三个栏是这样的： Example Table

我想什么做的是删除每一行针对DevReadType = XX和每一行与匹配设备号，但一个DevReadDate小于日当DevReadType =“XX ”。我一直无法找到这种复杂条件的例子。帮助将不胜感激！

Answer 1

如果我理解正确的话，我会建议沿着线的东西：

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 

您可以先运行选择againsr设备表测试你的where子句：

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