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;
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;
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 VOIDME 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 | 淘宝 | https://www.taobao.com/ | 13 | CN | | 3 | 小白教程 | http://www.voidme.com/ | 4689 | CN | | 4 | 微博 | http://weibo.com/ | 20 | CN | | 5 | Facebook | https://www.facebook.com/ | 3 | USA | | 7 | stackoverflow | http://stackoverflow.com/ | 0 | 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 | 2016-05-10 | | 2 | 3 | 100 | 2016-05-13 | | 3 | 1 | 230 | 2016-05-14 | | 4 | 2 | 10 | 2016-05-14 | | 5 | 5 | 205 | 2016-05-14 | | 6 | 4 | 13 | 2016-05-15 | | 7 | 3 | 220 | 2016-05-15 | | 8 | 5 | 545 | 2016-05-16 | | 9 | 3 | 201 | 2016-05-17 | +-----+---------+-------+------------+ 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:
实例
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:
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。