MySQL的UNION，为了通过日期时间从2个表

Question

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每个表（表1 &表2）有自己的时间字段。
我试图捕捉两个表的id，并按他们的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 

我的输出是不是跟这个尝试正确下令：

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 

所需数据：
从表2编号：2，1，从表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需要在每个查询上都有一个UNION。

Answer 2

您需要通过条款给每个子查询自己的订单：

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 

编辑 所以在这种情况下，你应该把在一列和秩序的所有日期时间由外条款

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