sql - 有子句中的SQL划分问题

Question

当我尝试这样做时

select first_name from employees 
group by salary,first_name
having salary between 0 and 4800

我收到了 49 条记录

当我尝试这样做时，我没有得到任何结果

select first_name from employees 
group by salary,first_name
having salary between 0 and (max(salary)/5)

这里select max(salary)/5 from employees fetches：4800

这很简单，但我不知道我在做什么愚蠢的错误

Answer 1

在这份声明中

select first_name from employees 
group by salary,first_name
having salary between 0 and (max(salary)/5)

您按薪水和名字分组，这很可能只按一行分组。您实际上是在寻找介于 0 和 X/5 之间的 X，这可能不会返回任何结果。

在这份声明中

select max(salary)/5 from employees fetches

你没有分组，所以你得到每个人的最高薪水。

我认为这

select first_name from employees 
WHERE salary between 0 and (SELECT max(salary) FROM employees)/5

是你要找的

Answer 2

您不能在 where 子句中使用聚合函数。

用这个：

select first_name from employees 
group by salary,first_name
having salary between 0 and (SELECT max(salary)/5 from employees)

Answer 3

我会使用子查询来避免第二次传递数据：

select first_name
from (select first_name
            ,salary
            ,max(salary) over () max_salary
      from employees)
where salary between 0 and max_salary/5
group by salary,first_name;

虽然我不知道你为什么按薪水和名字分组。