MySQL连接操作

MySQL的JOIN（一）：用法

上文的数据库栏目

两表连接，列名冲突

表结构如下：

mysql> select * from Customers;
+----+-------+
| Id | Name  |
+----+-------+
|  1 | Joe   |
|  2 | Henry |
|  3 | Sam   |
|  4 | Max   |
+----+-------+
4 rows in set (0.00 sec)

mysql> select * from orders;
+----+------------+
| Id | CustomerId |
+----+------------+
|  1 |          3 |
|  2 |          1 |
+----+------------+
2 rows in set (0.00 sec)

不使用as改名：

mysql> select Name from Customers left join orders on Customers.Id = orders.CustomerId where CustomerId is null;
+-------+
| Name  |
+-------+
| Henry |
| Max   |
+-------+
2 rows in set (0.00 sec)

使用as改名：

mysql> select Name as Customers from Customers left join orders on Customers.Id = orders.CustomerId where CustomerId is null;
+-----------+
| Customers |
+-----------+
| Henry     |
| Max       |
+-----------+
2 rows in set (0.00 sec)