MySQL全連線(Full Join）實現
阿新 • • 發佈：2019-01-27
MySQL本身不支援你所說的full join（全連線），但可以通過union來實現 ，
下面是一個簡單測試，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>
下面是一個簡單測試，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>