SQL 中的 INNER JOIN函数

INNER JOIN通过基于连接断言组合两个表(table1和table2)的列值来创建新的输出表，该查询将table1的每一行与table2的每一行进行比较，以找到满足join的所有行，当满足连接条件时，A和B的每个匹配行对的列值将合并为输出行。

INNER JOIN - 语法

INNER JOIN 的基本语法如下。

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

INNER JOIN - 示例

请考虑以下两个表。

表1 - 客户表(CUSTOMERS)如下。

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

来源：LearnFk无涯教程网

+----+----------+-----+-----------+----------+
| 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INNER JOIN联接这两个表，如下所示:

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

这将产生以下输出。

+----+----------+--------+---------------------+
| ID | NAME     | AMOUNT | DATE                |
+----+----------+--------+---------------------+
|  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 |
+----+----------+--------+---------------------+