SQL - INNER JOINS

  • 简述

    最重要和最常用的连接是INNER JOIN. 它们也被称为EQUIJOIN.
    INNER JOIN 通过基于连接谓词组合两个表(table1 和 table2)的列值来创建一个新的结果表。该查询将 table1 的每一行与 table2 的每一行进行比较,以找到满足连接谓词的所有行对。当满足连接谓词时,将 A 和 B 的每对匹配行的列值组合成一个结果行。
  • 句法

    的基本语法INNER JOIN如下。
    
    SELECT table1.column1, table2.column2...
    FROM table1
    INNER JOIN table2
    ON table1.common_field = table2.common_field;
    
  • 例子

    考虑以下两个表。
    Table 1− CUSTOMERS 表如下。
    
    +----+----------+-----+-----------+----------+
    | 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 | Muffy    |  24 | Indore    | 10000.00 |
    +----+----------+-----+-----------+----------+
    
    Table 2− ORDERS 表如下。
    
    +-----+---------------------+-------------+--------+
    | OID | DATE                | CUSTOMER_ID | AMOUNT |
    +-----+---------------------+-------------+--------+
    | 102 | 2009-10-08 00:00:00 |           3 |   3000 |
    | 100 | 2009-10-08 00:00:00 |           3 |   1500 |
    | 101 | 2009-11-20 00:00:00 |           2 |   1560 |
    | 103 | 2008-05-20 00:00:00 |           4 |   2060 |
    +-----+---------------------+-------------+--------+
    
    现在,让我们使用 INNER JOIN 连接这两个表,如下所示 -
    
    SQL> SELECT  ID, NAME, AMOUNT, DATE
       FROM CUSTOMERS
       INNER JOIN ORDERS
       ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;
    
    这将产生以下结果。
    
    +----+----------+--------+---------------------+
    | ID | NAME     | AMOUNT | DATE                |
    +----+----------+--------+---------------------+
    |  3 | kaushik  |   3000 | 2009-10-08 00:00:00 |
    |  3 | kaushik  |   1500 | 2009-10-08 00:00:00 |
    |  2 | Khilan   |   1560 | 2009-11-20 00:00:00 |
    |  4 | Chaitali |   2060 | 2008-05-20 00:00:00 |
    +----+----------+--------+---------------------+