Question

在下面的代码中，如果我用where子句替换having子句，我会在where子句中得到1054错误说明未知列tsal。为什么？还请特别指出我必须使用的情况以及我必须使用where子句的地方。

select employee_id,salary*months as tsal1
from Employee as h
having tsal1=(select max(e.tsal) as metsal
from (select employee_id,salary*months as tsal
from Employee) as e)

Answer 1

MySql确实not allow您要在select子句中引用别名（在where子句中定义）。

要解决此问题，只需重复该别名的表达式：

select employee_id, salary*months as tsal1
from   Employee as h
where salary*months=(select max(e.tsal) as metsal
                     from   (select employee_id,salary*months as tsal
                             from   Employee) as e)

注意：不需要有两个内部子查询。您可以简化为：

select employee_id, salary*months as tsal1
from   Employee as h
where  salary*months=(select max(salary*months) from Employee)

为什么where子句在我的sql查询中不起作用？

1 个答案: