Question

我在执行以下数据库查询时遇到问题。

我正在使用Oracle 11g企业版

查询1：

SELECT d.department_id, max(salary), min(salary), avg(salary), count(*) no_of_employees
FROM departments d, employees e
WHERE e.department_id = d.department_id
GROUP BY d.department_id

结果：成功输出

查询2：

SELECT d.department_id, d.department_name, max(salary), min(salary), avg(salary), count(*) no_of_employees
FROM departments d, employees e
WHERE e.department_id = d.department_id
GROUP BY d.department_id

结果：

ORA-00979：不是GROUP BY表达式

有人可以帮我解决这个问题吗？请告诉我这个表达方式有什么问题。

Answer 1

您还必须按department_name分组

Answer 2

您需要GROUP BY所有没有聚合函数的列（MAX，COUNT等）。因此：

select d.department_id
     , d.department_name
     , max(salary), min(salary), avg(salary) , count(*) no_of_employees
from departments d, employees e
where e.department_id = d.department_id
group by d.department_id, d.department_name;

但你也应该考虑做一个ANSI连接：

select department_id
     , department_name
     , max(salary), min(salary), avg(salary) , count(*) no_of_employees
from departments
join employees USING (department_id)
group by department_id, department_name;

我在执行以下数据库查询时遇到问题

2 个答案: