SQL INNER JOIN

SQL INNER JOIN 关键字

INNER JOIN 关键字在表中存在至少一个匹配时返回行。

SQL INNER JOIN 语法

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name=table2.column_name;

或：

SELECT column_name(s)
FROM table1
JOIN table2
ON table1.column_name=table2.column_name;

注释：INNER JOIN 与 JOIN 是相同的。

演示数据库

在本教程中，我们将使用 runoops样本数据库。

下面是选自 “websites” 表的数据：

+----+----------------+---------------------------+-------+---------+
| id | name           | url                       | alexa | country |
+----+----------------+---------------------------+-------+---------+
|  1 | Google          | https://www.google.cm/    |     1 | USA     |
|  2 | Amazon         | https://z.cn/             |     2 | USA     |
|  3 | 淘宝           | https://www.taobao.com/   |    10 | CN      |
|  4 | 自学教程       | http://runoops.com/       |  5787 | CN      |
|  5 | 微博           | http://weibo.com/         |    18 | CN      |
|  6 | stackoverflow  | http://stackoverflow.com/ |    66 | IND     |
+----+----------------+---------------------------+-------+---------+

下面是 “access_log” 网站访问记录表的数据：

mysql> SELECT * FROM access_log;
+-----+---------+-------+------------+
| aid | site_id | count | date       |
+-----+---------+-------+------------+
|   1 |       1 |    45 | 2020-05-10 |
|   2 |       3 |   100 | 2020-05-13 |
|   3 |       1 |   230 | 2020-05-14 |
|   4 |       2 |    10 | 2020-05-14 |
|   5 |       5 |   205 | 2020-05-14 |
|   6 |       4 |    13 | 2020-05-15 |
|   7 |       3 |   220 | 2020-05-15 |
|   8 |       5 |   545 | 2020-05-16 |
|   9 |       3 |   201 | 2020-05-17 |
+-----+---------+-------+------------+
9 rows in set (0.00 sec)

SQL INNER JOIN 实例

下面的 SQL 语句将返回所有网站的访问记录：

SELECT websites.name, access_log.count, access_log.date
FROM websites
INNER JOIN access_log
ON websites.id=access_log.site_id
ORDER BY access_log.count;

执行以上 SQL 输出结果如下：

mysql> SELECT websites.name, access_log.count, access_log.date
    -> FROM websites
    -> INNER JOIN access_log
    -> ON websites.id=access_log.site_id
    -> ORDER BY access_log.count;
+--------------+-------+------------+
| name         | count | date       |
+--------------+-------+------------+
| Amazon       |    10 | 2020-05-14 |
| 自学教程     |    13 | 2020-05-15 |
| Goole        |    45 | 2020-05-10 |
| 淘宝         |   100 | 2020-05-13 |
| 淘宝         |   201 | 2020-05-17 |
| 微博         |   205 | 2020-05-14 |
| 淘宝         |   220 | 2020-05-15 |
| Goole        |   230 | 2020-05-14 |
| 微博         |   545 | 2020-05-16 |
+--------------+-------+------------+
9 rows in set (0.00 sec)

注释：INNER JOIN 关键字在表中存在至少一个匹配时返回行。如果 "websites" 表中的行在 "access_log" 中没有匹配，则不会列出这些行。