如何解决从LeftJoin的MAX值的子查询
我在sql Server中有此查询，我想知道它是否可以更短？
我对所有列进行了一个子查询（带有group by），只是为了获得3个日期的MAX（）值，这些值来自左连接表。
SELECT otherCol1,otherCol2,MAX(UnsubscribedDate) AS UnsubscribedDate,MAX(OpenedDate) AS OpenedDate,MAX(ClickedDate) AS ClickedDate
FROM (
SELECT otherCol1,tu.JoinDate AS UnsubscribedDate,trkOp.Clicktime AS OpenedDate,trkRes.Clicktime AS ClickedDate
FROM v_members_email_occurrence vmec
LEFT JOIN tracking_unsubscribed tu WITH (NOLOCK) ON tu.ReportId = vmec.SendingId
LEFT JOIN tracking_opened trkOp WITH (NOLOCK) ON trkOp.ReportId = vmec.SendingId
LEFT JOIN tracking_result trkRes WITH (NOLOCK) ON trkRes.ReportId = vmec.SendingId
WHERE vmec.MemberId = @MemberId
) AS Result
GROUP BY otherCol1,otherCol2
解决方法
您可以聚合而无需子查询：
SELECT otherCol1,otherCol2,MAX(tu.JoinDate) AS UnsubscribedDate,MAX(trkOp.Clicktime) AS OpenedDate,MAX(trkRes.Clicktime) AS ClickedDate
FROM v_members_email_occurrence vmec
LEFT JOIN tracking_unsubscribed tu WITH (NOLOCK) ON tu.ReportId = vmec.SendingId
LEFT JOIN tracking_opened trkOp WITH (NOLOCK) ON trkOp.ReportId = vmec.SendingId
LEFT JOIN tracking_result trkRes WITH (NOLOCK) ON trkRes.ReportId = vmec.SendingId
WHERE vmec.MemberId = @MemberId
GROUP BY otherCol1,otherCol2
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