Question

我遇到了一个查询，我无法让它正常工作。

这就是我需要做的事情：

编写一个将返回最大和最小平均值的查询按雇员表格按部门分组的工资。

这就是我所做的：

SELECT
(SELECT AVG(MIN(salary)) FROM employees GROUP BY department_id) As "Minimum Average salary",
(SELECT AVG(MAX(salary)) FROM employees GROUP BY department_id) As "Maximum Average Salary"
FROM EMPLOYEES

但它不断返回我超过1行的结果。我不能使用LIMIT 2，如果我用LIMIT查询，我会收到错误。

我也尝试过以下查询，但是我收到错误：缺少表达式。

SELECT
AVG(SELECT MIN(salary) FROM employees GROUP BY department_id)) As "Minimum Average salary",
AVG((SELECT MAX(salary) FROM employees GROUP BY department_id)) As "Maximum Average Salary"
FROM EMPLOYEES

Answer 1

无需内联视图 - 这有效：

select
  min(avg(salary)),
  max(avg(salary))
from
 employees
group by
  dept_id;

http://sqlfiddle.com/#!4/eff67/3

Answer 2

使用子查询检索所有平均工资。然后外部查询可以获取最小值和最大值：

select  min(AvgSalary)
,       max(AvgSalary)
from    (
        select  avg(salary) as AvgSalary
        from    employees
        group by
                department_id
        ) SubQueryAlias

Answer 3

首先，它很简单，为什么它返回的数量与EMPLOYEES表中的所有记录一样多;因为group by位于您的内部子查询中，而不会应用于您的主查询。实际上，对表中的每一行执行子查询，并且每行返回结果。我认为这是您需要的正确查询：

SELECT AVG(min_salary) As "Minimum Average salary", AVG(max_salary) As "Maximum Average Salary"
FROM
(SELECT MIN(salary) As min_salary, MAX(salary) AS max_salary
 FROM EMPLOYEES
 GROUP BY department_id
)

Answer 4

select MAX(salary),min(salary), avg(salary), department_id from employees  group by department_id

Oracle SQL为什么查询返回多个结果？

4 个答案: