SQL RIGHT JOIN 关键字

SQL RIGHT JOIN 关键字SQL RIGHT JOIN 关键字RIGHT JOIN 关键字从右表（table2）返回所有的行，即使左表（table1）中没有匹配。如果左表中没有匹配，则结果为 NULL。SQL RIGHT JOIN 语法SELECT column_name(s)FROM table1RIGHT JOIN table2ON table1.column_name=table2.column_name;或：SELECT column_name(s)FROM table1RIGHT OUTER JOIN table2ON table1.column_name=table2.column_name;注释：在某些数据库中，RIGHT JOIN 称为 RIGHT OUTER JOIN。演示数据库在本教程中，我们将使用 RUNOOB 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 | k88.net | http:





//www.k88.net/ | 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 RIGHT JOIN 实例下面的 SQL 语句将返回网站的访问记录。以下实例中我们把 access_log 作为左表，Websites 作为右表：实例SELECT Websites.name, access_log.count, access_log.dateFROM access_logRIGHT JOIN WebsitesON access_log.site_id=Websites.idORDER BY access_log.count DESC;执行以上 SQL 输出结果如下：注释：RIGHT JOIN 关键字从右表（Websites）返回所有的行，即使左表（access_log）中没有匹配。