来自 LeftJoin 的 MAX() 值的子查询

Posted 2023-03-31

【中文标题】来自 LeftJoin 的 MAX() 值的子查询

【英文标题】：Subquery for MAX() value from LeftJoin

【发布时间】：2020-11-05 15:12:53

【问题描述】：

我在 SQL Server 中有这个查询，我想知道它是否可以更短？

我已经对所有列进行了子查询（带有分组依据），只是为了获取来自表左连接的 3 个日期的 MAX() 值。

我想我不能没有子查询来获取 3 个日期的 MAX()。

SELECT otherCol1
    ,otherCol2 
    ,MAX(UnsubscribedDate) AS UnsubscribedDate
    ,MAX(OpenedDate) AS OpenedDate
    ,MAX(ClickedDate) AS ClickedDate
FROM (
    SELECT otherCol1
        ,otherCol2
        ,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

【参考方案1】：

您可以在没有子查询的情况下进行聚合：

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