Question

我需要在不同的表中从一堆不同的日期获取MAX日期。我有一个查询返回6个日期。我需要以某种方式获得该查询的最大值。这是我的第一个查询，它提供了6个不同的MAX日期：

    SELECT  
        MAX(mi.last_updated_dts),
        (SELECT MAX(lt.created_dts) FROM live_training as lt WHERE lt.me_id = 1156),
        (SELECT MAX(gm.created_dts) FROM group_member as gm WHERE gm.me_id = 1156),
        (SELECT MAX(clm.created_dts) FROM contact_list_member as clm WHERE clm.me_id = 1156),
        (SELECT MAX(mc.created_dts) FROM member_case as mc WHERE mc.me_id = 1156),
        (SELECT MAX(mcc.created_dts) FROM member_case_comment as mcc INNER JOIN member_case as mc ON (mcc.member_case_id = mc.id) WHERE mc.me_id = 1156)
    FROM 
        member_info AS mi
    WHERE mi.id = 1276

这是我正在尝试做的事情，但它不起作用：

SELECT MAX(
             SELECT  
                  MAX(mi.last_updated_dts),
                  (SELECT MAX(lt.created_dts) FROM live_training as lt WHERE lt.me_id = 1156),
                  (SELECT MAX(gm.created_dts) FROM group_member as gm WHERE gm.me_id = 1156),
                  (SELECT MAX(clm.created_dts) FROM contact_list_member as clm WHERE clm.me_id = 1156),
                  (SELECT MAX(mc.created_dts) FROM member_case as mc WHERE mc.me_id = 1156),
                  (SELECT MAX(mcc.created_dts) FROM member_case_comment as mcc INNER JOIN member_case as mc ON (mcc.member_case_id = mc.id) WHERE mc.me_id =1156)
             FROM 
                  member_info AS mi
             WHERE mi.id = 1276
          ) as theMostMaxDate

我不知道在声明中放什么，或者甚至可能。谢谢你的帮助！

Answer 1

一个解决方案可能是重写查询以在派生表中使用union all并从中获取最大值，尽管这只会得到一个日期而没有关于它的来源的信息（但如果是重要的是，您可以添加一个文字值列，指示哪个查询为您提供了最大日期）：

SELECT MAX(max_date) 
FROM (
    SELECT MAX(mi.last_updated_dts) AS max_date FROM member_info AS mi WHERE mi.id = 1276
    UNION ALL
    SELECT MAX(lt.created_dts) FROM live_training as lt WHERE lt.me_id = 1156
    UNION ALL
    SELECT MAX(gm.created_dts) FROM group_member as gm WHERE gm.me_id = 1156
    UNION ALL
    SELECT MAX(clm.created_dts) FROM contact_list_member as clm WHERE clm.me_id = 1156
    UNION ALL
    SELECT MAX(mc.created_dts) FROM member_case as mc WHERE mc.me_id = 1156
    UNION ALL
    SELECT MAX(mcc.created_dts) FROM member_case_comment as mcc 
    INNER JOIN member_case as mc ON (mcc.member_case_id = mc.id) WHERE mc.me_id = 1156
) t

Answer 2

Max（）是按功能分组，适用于单个字段或表达式。改为使用greates()函数，它适用于多个字段或表达式。

SELECT  
    GREATEST(MAX(mi.last_updated_dts),
    (SELECT MAX(lt.created_dts) FROM live_training as lt WHERE lt.me_id = 1156),
    (SELECT MAX(gm.created_dts) FROM group_member as gm WHERE gm.me_id = 1156),
    (SELECT MAX(clm.created_dts) FROM contact_list_member as clm WHERE clm.me_id = 1156),
    (SELECT MAX(mc.created_dts) FROM member_case as mc WHERE mc.me_id = 1156),
    (SELECT MAX(mcc.created_dts) FROM member_case_comment as mcc INNER JOIN member_case as mc ON (mcc.member_case_id = mc.id) WHERE mc.me_id = 1156)) as maxdate
FROM 
    member_info AS mi
WHERE mi.id = 1276

另一种解决方案是将独立查询与union结合使用，您可以使用max（）从结果集中选择总体最大值。

Answer 3

@jpw有针对此问题的正确解决方案。我只想指出你可以在没有子查询的情况下做到这一点：

403 forbidden error

如何从最大日期子查询列表中选择最大日期

3 个答案: