如何從最大日期子查詢列表中選擇最大日期

Question

我需要從不同日期的一堆日期中獲取MAX日期。我有一個查詢返回6個日期。我需要以某種方式獲得該查詢的最大值。這是我的作品，給我6個不同的MAX日期第一個查詢：

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 

這裏是什麼樣的，我試圖做的，但它不工作：

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 

我不不知道應該從何聲明中輸入什麼，或者甚至可能。謝謝你的幫助！

Answer 1

一個解決方案可能是重寫查詢以在派生表中使用union all並從中獲取最大值，儘管這隻會得到一個日期而沒有關於其來源的信息（但如果這很重要，您可以添加一列與一個文字值指示查詢什麼給你最大日期）：

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（）是一組由功能和工作在一個單一的字段或表達式。使用greates()函數可以在多個字段或表達式中工作。

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 

另一種解決方案是將獨立查詢與union結合起來，並且可以使用max（）從結果集中選擇總體最大值。

Answer 3

@jpw對此問題有正確的解決方案。我只是想指出的是，你可以不用子查詢：

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 
ORDER BY max_date DESC 
LIMIT 1;