SQL FULL JOIN

SQL FULL JOIN 是 LEFT JOIN 和 RIGHT JOIN 结果的合集。

连接表将包含两个表中的所有记录，并为任一侧丢失的匹配项填充 NULL。

语法

FULL JOIN的基本语法如下 -

SELECT table1.column1, table2.column2...
FROM table1
FULL JOIN table2
ON table1.common_field = table2.common_field;

在这里，给定的条件可以是基于我们要求的任何给定的表达式。

示例

现在我们看如下的两张表

1. CUSTOMERS 表

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
|  7 | Muffy    |  24 | Indore    | 10000.00 |
+----+----------+-----+-----------+----------+

2. ORDERS 表

+-----+---------------------+-------------+--------+
| OID | DATE                | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 100 | 2009-10-08 00:00:00 |           3 |   1500 |
| 101 | 2009-11-20 00:00:00 |           3 |   1560 |
| 102 | 2009-10-08 00:00:00 |           3 |   3000 |
| 103 | 2008-05-20 00:00:00 |           4 |   2060 |
| 104 | 2008-05-21 00:00:00 |           9 |   2160 |
+-----+---------------------+-------------+--------+

现在，让我们使用 FULL JOIN 连接这两个表，如下所示。

SQL> SELECT  ID, NAME, AMOUNT, DATE
   FROM CUSTOMERS
   FULL JOIN ORDERS
   ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;

结果如下：

+------+----------+--------+---------------------+
| ID   | NAME     | AMOUNT | DATE                |
+------+----------+--------+---------------------+
|    3 | kaushik  |   1500 | 2009-10-08 00:00:00 |
|    3 | kaushik  |   1560 | 2009-11-20 00:00:00 |
|    3 | kaushik  |   3000 | 2009-10-08 00:00:00 |
|    4 | Chaitali |   2060 | 2008-05-20 00:00:00 |
|    1 | Ramesh   |   NULL | NULL                |
|    2 | Khilan   |   NULL | NULL                |
|    5 | Hardik   |   NULL | NULL                |
|    6 | Komal    |   NULL | NULL                |
|    7 | Muffy    |   NULL | NULL                |
|    3 | kaushik  |   1500 | 2009-10-08 00:00:00 |
|    3 | kaushik  |   1560 | 2009-11-20 00:00:00 |
|    3 | kaushik  |   3000 | 2009-10-08 00:00:00 |
|    4 | Chaitali |   2060 | 2008-05-20 00:00:00 |
| NULL | NULL     |   2160 | 2008-05-21 00:00:00 |
+------+----------+--------+---------------------+

如果你当前使用的数据库不支持 FULL JOIN（MySQL 不支持 FULL JOIN），那么可以使用UNION ALL子句将这两个 JOIN 组合在一起，如下所示。

SQL> SELECT  ID, NAME, AMOUNT, DATE
   FROM CUSTOMERS
   LEFT JOIN ORDERS
   ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
UNION ALL
   SELECT  ID, NAME, AMOUNT, DATE
   FROM CUSTOMERS
   RIGHT JOIN ORDERS
   ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID

结果如下图所示