MySQL的UNION，爲了通過日期時間從2個表

Question

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每個表（表1 &表2）有自己的時間字段。
我試圖捕捉兩個表的id，並按他們的DATETIME字段排序。

例子：

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 

我的輸出是不是跟這個嘗試正確下令：

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 

所需數據：
從表2編號：2，1，從表1中
id：3，2，1
So：2，1，3，2，1

Answer 1

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 
ORDER BY table2.datetime2 DESC 

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 
ORDER BY table1.datetime1 DESC 

ORDER BY需要在每個查詢上都有一個UNION。

Answer 2

您需要通過條款給每個子查詢自己的訂單：

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 
    ORDER BY table1.datetime1 DESC 
    )t1 

    UNION ALL SELECT * 
    FROM (
    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 
    ORDER BY table2.datetime2 DESC 
    ) t2 

編輯 所以在這種情況下，你應該把在一列和秩序的所有日期時間由外條款

在

 SELECT * 
FROM (
    SELECT 
    1 AS selection, 
    table1.id, table1.datetime1 as dtime, 
    table3.user 
    FROM Table1 
    LEFT OUTER JOIN table2 
    ON table1.id = table2.table1id 
    LEFT OUTER JOIN table3 
    ON table1.id = table3.id 
    )t1 

    UNION ALL SELECT * 
    FROM (
    SELECT 
    2 AS selection, 
    table1.id, 
    table2.datetime2 
    table3.user 
    FROM Table1 
    INNER JOIN table2 
    ON table1.id = table2.table1id 
    INNER JOIN table3 
    ON table1.id = table3.id 
    ) t2 

    ORDER BY dtime DESC