MySQL数据库查询数据操作篇第二十四为表和字段取别名

24.为表和字段取别名

为表取别名
mysql> select * from orders as o
    -> where o.o_num = 3001;
+-------+---------------------+------+
| o_num | o_date              | c_id |
+-------+---------------------+------+
|  3001 | 2019-12-11 00:00:00 | 1001 |
+-------+---------------------+------+
1 row in set

mysql> select c.c_id,o.o_num
    -> from customers as c left outer join orders as o
    -> on c.c_id = o.c_id;
+-------+-------+
| c_id  | o_num |
+-------+-------+
| 10086 | NULL  |
| 10087 | NULL  |
| 10088 | NULL  |
+-------+-------+
3 rows in set

mysql> select f1.f_id,f1.f_name
    -> from fruits as f1,fruits as f2
    -> where f1.s_id = f2.s_id and f2.f_id = "a1";
+------+--------+
| f_id | f_name |
+------+--------+
| a1   | apple  |
+------+--------+
1 row in set

为字段取别名：
mysql> select f1.f_name as fruit_name,f1.f_price as fruit_price
    -> from fruits as f1
    -> where f1.f_price < 8;
+------------+-------------+
| fruit_name | fruit_price |
+------------+-------------+
| apple      | 5.2         |
| banana     | 6.2         |
| caomei     | 7.2         |
+------------+-------------+
3 rows in set