MySQL聯合查詢，按2個變量排序

Question

每個表（table1 & table2）都有自己的DATETIME字段。
我試圖捕捉兩個表的id，並按他們的DATETIME字段排序。

實施例：

Table 1      Table 2 
------------     ------------- 
id | datetime1    id | table1id | datetime2 
------------------------  ----------------------- 
1 | 2014-09-21 20:31:26  1 | 2   | 2014-09-21 20:31:29 
2 | 2014-09-21 20:31:27  2 | 3   | 2014-09-21 20:31:30 
3 | 2014-09-21 20:31:28 

Table 3      
------------    
id | user    
------------------------ 
2 | phil     
3 | nathalie 

我的輸出不與此查詢正確排序：

SELECT * 
FROM (
    SELECT 
    1 AS selection, 
    table1.id, table1.datetime1, 
    table2.datetime2 
    table3.user 
    FROM Table1 
    LEFT OUTER JOIN table2 
    ON table1.id = table2.table1id 
    LEFT OUTER JOIN table3 
    ON table1.id = table3.id 

    UNION ALL 

    SELECT 
    2 AS selection, 
    table1.id, table1.datetime1, 
    table2.datetime2 
    table3.user 
    FROM Table1 
    INNER JOIN table2 
    ON table1.id = table2.table1id 
    INNER JOIN table3 
    ON table1.id = table3.id 
) AS query 
ORDER BY table1.datetime1 DESC, table2.datetime2 DESC 

期望的數據：
從表2 ID：2，1，
從表1 id：3，2，1
So：2，1，3，2，1

////編輯

對於那些可能需要長時間和複雜的MySQL請求而苦惱的人，請在PhpmyAdmin嘗試！它會告訴你錯誤！

////編輯

Answer 1

你真正需要做的是更仔細考慮您的架構。考慮命名的日期時間列相同，然後運行一個查詢這樣的 - http://sqlfiddle.com/#!2/a3b4c/7/0

SELECT selection, id, datetimefoo, user FROM (
    SELECT 
    1 AS selection, 
    table1.id, table1.datetimefoo, 
    table3.user 
    FROM table1 
    LEFT OUTER JOIN table2 
    ON table1.id = table2.table1id 
    LEFT OUTER JOIN table3 
    ON table1.id = table3.id 


    UNION 

    SELECT 
    2 AS selection, 
    table1.id, table1.datetimefoo, 
    table3.user 
    FROM table1 
    INNER JOIN table2 
    ON table1.id = table2.table1id 
    INNER JOIN table3 
    ON table1.id = table3.id 

) AS T2 
ORDER BY datetimefoo DESC 

在SQL撥弄這將產生的結果更接近你在找什麼。我仍然不確定你爲什麼需要第二個查詢中的INNER JOINS，但是這裏沒有你在做的事情。

這裏是不需要的列名的變化的另一種方法，但需要排序的列一個別名 - http://sqlfiddle.com/#!2/ec4bc/3/0

SELECT * FROM (
    SELECT 
    1 AS selection, 
    table1.id, table1.datetimefoo AS sort_date, -- alias on first table's date 
    table2.datetimebar, 
    table3.user 
    FROM table1 
    LEFT OUTER JOIN table2 
    ON table1.id = table2.table1id 
    LEFT OUTER JOIN table3 
    ON table1.id = table3.id 


    UNION 

    SELECT 
    2 AS selection, 
    table1.id, table1.datetimefoo, 
    table2.datetimebar AS sort_date, -- alias on second table's date 
    table3.user 
    FROM table1 
    INNER JOIN table2 
    ON table1.id = table2.table1id 
    INNER JOIN table3 
    ON table1.id = table3.id 

) AS T2 
ORDER BY sort_date DESC 

Answer 2

我相信你是過於複雜一個相當簡單的任務：

SELECT * 
FROM (
    SELECT 1 AS selection, table1.id as id, table1.datetime1 as date FROM Table1 
    UNION ALL 
    SELECT 2 AS selection, table2.id as id, table2.datetime2 as date FROM Table2 
) AS query 
ORDER BY date DESC