如何在MySQL中进行完全外部联接？

我想在MySQL中进行完全的外部连接。这可能吗？MySQL是否支持完全外部联接？

当前回答

Use:

SELECT * FROM t1 FULL OUTER JOIN t2 ON t1.id = t2.id;

可以按如下方式重新创建：

 SELECT t1.*, t2.*
 FROM (SELECT * FROM t1 UNION SELECT name FROM t2) tmp
 LEFT JOIN t1 ON t1.id = tmp.id
 LEFT JOIN t2 ON t2.id = tmp.id;

使用UNION或UNION ALL答案不能涵盖基表具有重复条目的边缘情况。

说明：

UNION或UNION ALL无法覆盖边缘情况。我们无法在MySQL上测试这一点，因为它不支持完整的外部连接，但我们可以在一个支持它的数据库上说明这一点：

 WITH cte_t1 AS
 (
     SELECT 1 AS id1
     UNION ALL SELECT 2
     UNION ALL SELECT 5
     UNION ALL SELECT 6
     UNION ALL SELECT 6
 ),
cte_t2 AS
(
     SELECT 3 AS id2
     UNION ALL SELECT 4
     UNION ALL SELECT 5
     UNION ALL SELECT 6
     UNION ALL SELECT 6
)
SELECT  *  FROM  cte_t1 t1 FULL OUTER JOIN cte_t2 t2 ON t1.id1 = t2.id2;

这给了我们这样的答案：

id1  id2
1  NULL
2  NULL
NULL  3
NULL  4
5  5
6  6
6  6
6  6
6  6

UNION解决方案：

SELECT  * FROM  cte_t1 t1 LEFT OUTER JOIN cte_t2 t2 ON t1.id1 = t2.id2
UNION    
SELECT  * FROM cte_t1 t1 RIGHT OUTER JOIN cte_t2 t2 ON t1.id1 = t2.id2

给出错误答案：

 id1  id2
NULL  3
NULL  4
1  NULL
2  NULL
5  5
6  6

UNION ALL解决方案：

SELECT  * FROM cte_t1 t1 LEFT OUTER join cte_t2 t2 ON t1.id1 = t2.id2
UNION ALL
SELECT  * FROM  cte_t1 t1 RIGHT OUTER JOIN cte_t2 t2 ON t1.id1 = t2.id2

也不正确。

id1  id2
1  NULL
2  NULL
5  5
6  6
6  6
6  6
6  6
NULL  3
NULL  4
5  5
6  6
6  6
6  6
6  6

鉴于此查询：

SELECT t1.*, t2.*
FROM (SELECT * FROM t1 UNION SELECT name FROM t2) tmp
LEFT JOIN t1 ON t1.id = tmp.id
LEFT JOIN t2 ON t2.id = tmp.id;

给出以下内容：

id1  id2
1  NULL
2  NULL
NULL  3
NULL  4
5  5
6  6
6  6
6  6
6  6

顺序不同，但在其他方面与正确答案匹配。

2017-02-09 14:29:57

其他回答

使用交叉联接解决方案：

SELECT t1.*, t2.*
FROM table1 t1
INNER JOIN table2 t2 
ON 1=1;

2017-06-13 19:53:53

SELECT
    a.name,
    b.title
FROM
    author AS a
LEFT JOIN
    book AS b
    ON a.id = b.author_id
UNION
SELECT
    a.name,
    b.title
FROM
    author AS a
RIGHT JOIN
    book AS b
    ON a.id = b.author_id

2013-10-24 11:10:07

这也是可能的，但您必须在select中提到相同的字段名。

SELECT t1.name, t2.name FROM t1
LEFT JOIN t2 ON t1.id = t2.id
UNION
SELECT t1.name, t2.name FROM t2
LEFT JOIN t1 ON t1.id = t2.id

2014-02-03 12:30:07