测试where语句,第二种语句返回0行数据
```sql
select e.* from
(select name, salary, deductions["Federal Taxes"] as ded,
salary * (1 - deductions["Federal Taxes"]) as salary_minus_fed_taxes from employees) e
where round(e.salary_minus_fed_taxes) > 70000;
------------------------结果-------------------------------
+------------+-----------+--------+---------------------------+
| e.name | e.salary | e.ded | e.salary_minus_fed_taxes |
+------------+-----------+--------+---------------------------+
| John Doe | 100000.0 | 0.2 | 80000.0 |
| John Bob | 300000.0 | 0.4 | 180000.0 |
| John Bill | 200000.0 | 0.3 | 140000.0 |
+------------+-----------+--------+---------------------------+
----------------------------第二种方式:
select name, salary, deductions["Federal Taxes"] as ded,
salary * (1 - deductions["Federal Taxes"]) as salary_minus_fed_taxes from employees
where (select salary * (1 - deductions["Federal Taxes"]) from employees) = 80000.0;
----------------结果--------------------------------------
+-------+---------+------+-------------------------+
| name | salary | ded | salary_minus_fed_taxes |
+-------+---------+------+-------------------------+
+-------+---------+------+-------------------------+
where中又使用了一次emloyees表,和上面的emloyees表没有任何关联关系,你要根据80000.0来定位数据的话,应该是像下面这样写
select name, salary, deductions["Federal Taxes"] as ded,
salary * (1 - deductions["Federal Taxes"]) as salary_minus_fed_taxes from employees
where salary * (1 - deductions["Federal Taxes"]) = 80000.0;
当然我不确定你这个显示是否有小数位四舍五入,或许要改成
round(salary * (1 - deductions["Federal Taxes"]) ,1) = 80000.0