SQL FULL JOIN
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 table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;
FROM table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;
演示数据库
在本教程中，我们将使用 JSON 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.json.cn | 888 | 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.date
FROM Websites
FULL OUTER JOIN access_log
ON Websites.id=access_log.site_id
ORDER BY access_log.count DESC;
FROM Websites
FULL OUTER JOIN access_log
ON Websites.id=access_log.site_id
ORDER 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。