SQL FULL OUTER JOIN 关键字

SQL FULL OUTER JOIN 关键字SQL FULL OUTER JOIN 关键字FULL OUTER JOIN 关键字只要左表（table1）和右表（table2）其中一个表中存在匹配，则返回行.FULL OUTER JOIN 关键字结合了 LEFT JOIN 和 RIGHT JOIN 的结果。SQL FULL OUTER JOIN 语法SELECT column_name(s)FROM table1FULL OUTER JOIN table2ON table1.column_name=table2.column_name;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：+-----+---------+-------+------------+| 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 FULL OUTER JOIN 实例下面的 SQL 语句选取所有网站访问记录。MySQL中不支持 FULL OUTER JOIN，你可以在 SQL Server 测试以下实例。实例SELECT Websites.name, access_log.count, access_log.dateFROM WebsitesFULL OUTER JOIN access_logON Websites.id=access_log.site_idORDER BY access_log.count DESC;注释：FULL OUTER JOIN 关键字返回左表（Websites）和右表（access_log）中所有的行。如果 "Websites" 表中的行在 "access_log" 中没有匹配或者 "access_log" 表中的行在 "Websites" 表中没有匹配，也会列出这些行。