SELECT
MIN(sal),department_id
FROM
(SELECT
AVG(salary) AS sal,e.department_id
FROM
employees e
GROUP BY
department_id)
AS sal.d
为什么from后的子表中有的字段也不能查询呢,MIN(sal)显示正确,但是department_id显示为null
SELECT
MIN(sal),department_id
FROM
(SELECT
AVG(salary) AS sal,e.department_id
FROM
employees e
GROUP BY
department_id)
AS sal.d
为什么from后的子表中有的字段也不能查询呢,MIN(sal)显示正确,但是department_id显示为null
group by是按字段列表分组,所以只有在group by后面出现的字段才能在select里面出现。
比如按性别分组,统计男,女同学的人数,如果select里面出现了姓名字段,显然是没有意义的,也不符合逻辑。