MySQL全连接(Full Join）实现

MySQL本身不支持你所说的full join（全连接），但可以通过union来实现 ，
下面是一个简单测试，可以看看：

mysql> CREATE TABLE a(id int,name char(1));
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE b(id int,name char(1));
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO a VALUES(1,'a'),(2,'b');
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0

mysql> INSERT INTO b VALUES(2,'b'),(3,'c');
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0

mysql> SELECT * FROM a LEFT JOIN b ON a.id=b.id
-> UNION
-> SELECT * FROM a RIGHT JOIN b ON a.id=b.id;
+------+------+------+------+
| id | name | id | name |
+------+------+------+------+
| 1 | a | NULL | NULL |
| 2 | b | 2 | b |
| NULL | NULL | 3 | c |
+------+------+------+------+
3 rows in set (0.00 sec)
mysql>

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