SQL 全外連接
SQL FULL OUTER JOIN 關鍵字
FULL OUTER JOIN 關鍵字只要左表（table1）和右表（table2）其中一個表中存在匹配，則傳回行.
FULL OUTER JOIN 關鍵字結合了LEFT JOIN 和RIGHT JOIN 的結果。
SQL FULL OUTER JOIN 語法
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;
示範資料庫
在本教學中，我們將使用php 樣本資料庫。
下面是選自"Websites" 表的資料：
+----+--------------+--- ------------------------+-------+---------+
| id | name | url | alexa | country |
+----+----------+------------------------------------ --------+-------+---------+
| 1 | Google | https://www.google.cm/ | 1 | USA | 1 |
| 2 | 淘寶 | https://www.taobao.com/ | 13 | CN cn/ | 4689 | CN |
| 4 | 微博 | http://weibo.com/ | 201 https://www.facebook.com/ | 3 | USA |
| 7 | stackoverflow | http://stackoverflow.com/ | 0 | IND |
+----+---------------+----------- ------------------+-------+---------+
#
SQL FULL OUTER JOIN 實例下面的SQL 語句選取所有網站存取記錄。 MySQL中不支援 FULL OUTER JOIN，你可以在 SQL Server 測試下列實例。
#| id | name | url | alexa | country |
+----+----------+------------------------------------ --------+-------+---------+
| 1 | Google | https://www.google.cm/ | 1 | USA | 1 |
| 2 | 淘寶 | https://www.taobao.com/ | 13 | CN cn/ | 4689 | CN |
| 4 | 微博 | http://weibo.com/ | 201 https://www.facebook.com/ | 3 | USA |
| 7 | stackoverflow | http://stackoverflow.com/ | 0 | IND |
+----+---------------+----------- ------------------+-------+---------+
#
下面是"access_log" 網站存取記錄表的資料：
+-----+---------+-------+- -----------+
| aid | site_id | count | date |
+-----+---------+------ -+------------+
| 1 | 1 | 45 | 2016-05-10 1 | 45 | 2016-05-10 |
| 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)
| aid | site_id | count | date |
+-----+---------+------ -+------------+
| 1 | 1 | 45 | 2016-05-10 1 | 45 | 2016-05-10 |
| 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 實例下面的SQL 語句選取所有網站存取記錄。 MySQL中不支援 FULL OUTER JOIN，你可以在 SQL Server 測試下列實例。
範例
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;
FULL OUTER JOIN access_log
## ON Websites.id=access_log.site_id
ORDER BY access_log.count DESC;
註解：FULL OUTER JOIN 關鍵字傳回左表（Websites）和右表（access_log）中所有的行。如果 "Websites" 表中的行在 "access_log" 中沒有符合或 "access_log" 表中的行在 "Websites" 表中沒有匹配，也會列出這些行。
