Question

以下是我的查询，我想要的结果如下所示。我怎么能在mysql中这样做？

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
FULL JOIN Orders
ON Persons.P_Id=Orders.P_Id
ORDER BY Persons.LastName

结果集需要如下所示：

LastName      FirstName     OrderNo
Hansen        Ola          22456
Hansen        Ola          24562
Pettersen     Kari         77895
Pettersen     Kari         44678
Svendson      Tove   
                           34764

Answer 1

MySQL缺乏对FULL OUTER JOIN的支持。

因此，如果您想在MySQL上模拟完全加入，请查看here。

通常建议的解决方法如下所示：

SELECT  t_13.value AS val13, t_17.value AS val17
FROM    t_13
LEFT JOIN
        t_17
ON      t_13.value = t_17.value
UNION ALL
SELECT  t_13.value AS val13, t_17.value AS val17
FROM    t_13
RIGHT JOIN
        t_17
ON      t_13.value = t_17.value
WHERE   t_13.value IS NULL
ORDER BY
        COALESCE(val13, val17)
LIMIT 30

Answer 2

完整的mysql FULL [OUTER] JOIN有几种方法。

UNION左连接和右连接。 UNION将通过执行ORDER BY操作删除重复项。因此，根据您的数据，它可能不具备高性能。
```
 SELECT * FROM A 
   LEFT JOIN B ON A.key = B.key 

 UNION 

 SELECT * FROM A 
   RIGHT JOIN B ON A.key = B.key
```
UNION ALL左连接和右EXCLUDING连接（图中的右下图）。 UNION ALL不会删除重复项。有时这可能是您想要的行为。您还希望使用RIGHT EXCLUDING来避免重复选择A和选择B中的常见记录 - 即左连接已包含选择B中的常用记录，不允许使用右连接重复该记录。
```
 SELECT * FROM A 
   LEFT JOIN B ON A.key = B.key 

 UNION ALL

 SELECT * FROM A 
   RIGHT JOIN B ON A.key = B.key
   WHERE A.key IS NULL
```

Answer 3

SELECT  p.LastName, p.FirstName, o.OrderNo
FROM    persons AS p
LEFT JOIN
        orders AS o
ON      o.orderNo = p.p_id
UNION ALL
SELECT  NULL, NULL, orderNo
FROM    orders
WHERE   orderNo NOT IN
        (
        SELECT  p_id
        FROM    persons
        )

Answer 4

试试这个：

(SELECT p.LastName, p.FirstName, o.OrderNo
 FROM   Persons p
   LEFT JOIN Orders o
   ON o.OrderNo = p.P_id
)
UNION
(SELECT p.LastName, p.FirstName, o.OrderNo
 FROM   Persons p
   RIGHT JOIN Orders o
   ON o.OrderNo = p.P_id
);

+----------+-----------+---------+
| LastName | FirstName | OrderNo |
+----------+-----------+---------+
| Singh    | Shashi    |       1 |
| Yadav    | Sunil     |    NULL |
| Singh    | Satya     |    NULL |
| Jain     | Ankit     |    NULL |
| NULL     | NULL      |      11 |
| NULL     | NULL      |      12 |
| NULL     | NULL      |      13 |
+----------+-----------+---------+

Answer 5

嗯，将LEFT和RIGHT JOIN与UNION结合起来可以做到这一点：

SELECT  p.LastName, p.FirstName, o.OrderNo
FROM    persons AS p
LEFT JOIN
        orders AS o
ON      p.P_Id = Orders.P_Id
UNION ALL
SELECT  p.LastName, p.FirstName, o.OrderNo
FROM    persons AS p 
RIGHT JOIN
        orders AS o
ON      p.P_Id = Orders.P_Id
WHERE   p.P_Id IS NULL

Answer 6

完全加入mysql :(左联盟右）或（右联左）

 SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
    FROM Persons
    left JOIN Orders
    ON Persons.P_Id=Orders.P_Id
    ORDER BY Persons.LastName

    Union

    SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
    FROM Persons
    Right JOIN Orders
    ON Persons.P_Id=Orders.P_Id
    ORDER BY Persons.LastName

Answer 7

每个人都是正确的，但是两次编写相同的查询并不是编程的好方法... 所以我有另一种方法可以在mysql中进行完全连接，如下所示：

SELECT
 user_id , user_name, user_department 
FROM 
 (SELECT 
     user_id  , user_name , NULL as user_department 
  FROM
   tb_users 
 UNION 
   SELECT 
     user_id ,NULL as user_name , user_department
   FROM 
      tb_departments
 ) as t group by user_id

MySQL完全加入？

7 个答案: