备注:测试数据库版本为MySQL 8.0
如需要scott用户下建表及录入数据语句,可参考:
scott建表及录入数据sql脚本
我们写sql的过程中,经常会遇到别名的问题,也经常因为别名的问题报错
下面是一个where应用别名列的问题
-- where直接用别名列,报错
select sal as salary,co
from emp
where salary < 5000;
-- 用内联视图可以解决这个问题
select *
from (
select sal as salary,comm as commission
from emp
) x
where salary < 5000;
执行结果:
mysql> select sal as salary,comm as commission
-> from emp
-> where salary < 5000;
ERROR 1054 (42S22): Unknown column 'salary' in 'where clause'
mysql>
mysql>
mysql>
mysql> select *
-> from (
-> select sal as salary,comm as commission
-> from emp
-> ) x
-> where salary < 5000;
+---------+------------+
| salary | commission |
+---------+------------+
| 1600.00 | 1300.00 |
| 1250.00 | 1500.00 |
| 2975.00 | 500.00 |
| 1250.00 | 2400.00 |
| 2850.00 | 500.00 |
| 2450.00 | 500.00 |
| 3000.00 | 500.00 |
| 1500.00 | 0.00 |
| 1100.00 | 500.00 |
| 950.00 | 500.00 |
| 3000.00 | 500.00 |
| 1300.00 | 500.00 |
+---------+------------+
12 rows in set (0.01 sec)