Question

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每个表格（table1＆amp; table2）都有自己的DATETIME字段我正在尝试捕获两个表的id并按DATETIME字段对它们进行排序。

示例：

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

此尝试未正确输出我的输出：

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：
来自表2 id：2,1，
从表1 id：3,2,1 所以：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需要在每个查询上只有一个UNION。

Answer 2

您需要为每个子查询提供自己的order by子句：

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

修改所以在这种情况下，您应该将所有日期时间放在一个列中，并在外部子句

中排序
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

MySQL UNION，从2个表中按日期时间排序

2 个答案: