SQL 中的 FULL JOIN函数

SQL FULL JOIN 组合了左右外部联接的输出，联接的表将包含两个表中的所有记录，并为任一侧缺少的匹配项填充NULL。

FULL JOIN - 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;

FULL JOIN - 示例

请考虑以下两个表。

表1 -客户表(CUSTOMERS)如下。

+----+----------+-----+-----------+----------+
| 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 | Learnfk    |  24 | Indore    | 10000.00 |
+----+----------+-----+-----------+----------+

表2 -订单表(ORDERS)如下。

+-----+---------------------+-------------+--------+
|OID  | DATE                | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 102 | 2019-10-08 00:00:00 |           3 |   3000 |
| 100 | 2019-10-08 00:00:00 |           3 |   1500 |
| 101 | 2019-11-20 00:00:00 |           2 |   1560 |
| 103 | 2018-05-20 00:00:00 |           4 |   2060 |
+-----+---------------------+-------------+--------+

现在，让无涯教程使用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;

这将产生以下输出-

链接：https://www.learnfk.comhttps://www.learnfk.com/sql/sql-full-joins.html

来源：LearnFk无涯教程网

+------+----------+--------+---------------------+
| ID   | NAME     | AMOUNT | DATE                |
+------+----------+--------+---------------------+
|    1 | Ramesh   |   NULL | NULL                |
|    2 | Khilan   |   1560 | 2019-11-20 00:00:00 |
|    3 | kaushik  |   3000 | 2019-10-08 00:00:00 |
|    3 | kaushik  |   1500 | 2019-10-08 00:00:00 |
|    4 | Chaitali |   2060 | 2018-05-20 00:00:00 |
|    5 | Hardik   |   NULL | NULL                |
|    6 | Komal    |   NULL | NULL                |
|    7 | Learnfk    |   NULL | NULL                |
|    3 | kaushik  |   3000 | 2019-10-08 00:00:00 |
|    3 | kaushik  |   1500 | 2019-10-08 00:00:00 |
|    2 | Khilan   |   1560 | 2019-11-20 00:00:00 |
|    4 | Chaitali |   2060 | 2018-05-20 00:00:00 |
+------+----------+--------+---------------------+

如果您的数据库不支持FULL JOIN(MySQL不支持FULL JOIN)，则可以使用 UNION ALL 子句来组合这两个JOINS，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