mysql - 在 UNION 之后创建一列具有相同名称的列

Question

我有两张桌子：

Table1
id | col1 | col2 | other_id
---------------------------
1  | val1 | val2 | 2
2  | val3 | val4 | 3

Table2
id | col3 | other_id
--------------------
1  | val5 | 4

我想以这种方式加入这两个表：

id | col1 | col2 | col3 | other_id
-----------------------------------
1  | val1 | val2 | NULL | 2
2  | val3 | val4 | NULL | 3
1  | NULL | NULL | val5 | 4

我创建了这个 SQL 查询：

(
SELECT * FROM table1 AS M LEFT JOIN table2 AS D ON M.other_id = D.other_id
)
UNION
(
SELECT * FROM table1 AS M RIGHT JOIN table2 AS D ON M.other_id = D.other_id
)

结果：

id   | col1 | col2 | other_id | id   | col3 | other_id
------------------------------------------------------
1    | val1 | val2 | 2        | NULL | NULL | NULL
2    | val3 | val4 | 3        | NULL | NULL | NULL
NULL | NULL | NULL | NULL     | 1    | val5 | 4

但我得到多个具有相同标签的列。我不想使用别名，只需加入具有相同名称的列。

Answer 1

您可以使用UNION ALL它，只需为两个表中都不存在的列放置占位符：

select t1.id, t1.col1, t1.col2, null col3, t1.other_id
from table1 t1
union all
select t2.id, null col1, null col2, t2.col3, t2.other_id
from table2 t2

请参阅带有演示的 SQL Fiddle

结果：

| ID |   COL1 |   COL2 |   COL3 | OTHER_ID |
--------------------------------------------
|  1 |   val1 |   val2 | (null) |        2 |
|  2 |   val3 |   val4 | (null) |        3 |
|  1 | (null) | (null) |   val5 |        4 |

Answer 2

如果您想在不使用alias的情况下实现此目的，则必须手动使用每一列。

(SELECT M.ID,M.Col1,M.Col2,D.Col3,M.Other_ID 
   FROM table1 AS M 
   LEFT JOIN table2 AS D 
   ON M.other_id = D.other_id)
UNION
(SELECT D.ID,M.Col1,M.Col2,D.Col3,D.Other_ID 
   FROM table1 AS M 
   RIGHT JOIN table2 AS D 
   ON M.other_id = D.other_id);

看到这个 SQLFiddle

结果

| ID |   COL1 |   COL2 |   COL3 | OTHER_ID |
--------------------------------------------
|  1 |   val1 |   val2 | (null) |        2 |
|  2 |   val3 |   val4 | (null) |        3 |
|  1 | (null) | (null) |   val5 |        4 |

Answer 3

SELECT id, col1, col2, ''  col3, other_id
FROM table1 

UNION

SELECT id, '' col1 , '' col2, col3, other_id 
FROM table2

Answer 4

Union 希望这些表具有相同的字段。您可以放置​​“人工”字段来做到这一点