sql使用GROUPBY不仅仅是一个表

我试图得到所有部门的工资，他们的位置，员工人数和平均工资。我尝试过类似的方法，但出现了一个“非表达式分组”错误：

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我从未在多个表上使用过group by，因此如果有人能解释如何使用它或我做错了什么，我将不胜感激。

您需要在

group by

子句中添加非聚合字段

试着这样做：

 SELECT d.DEPARTMENT_NAME, l.CITY, count(e.FIRST_NAME), avg(e.SALARY)
   FROM DEPARTMENTS d, LOCATIONS l, EMPLOYEES e
  WHERE d.DEPARTMENT_ID = e.DEPARTMENT_ID
    AND d.LOCATION_ID = l.LOCATION_ID
  GROUP BY d.DEPARTMENT_NAME, l.CITY

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正确的SQL应该是：

 SELECT d.DEPARTMENT_NAME, l.CITY, count(e.FIRST_NAME), avg(e.SALARY)
   FROM DEPARTMENTS d, LOCATIONS l, EMPLOYEES e
  WHERE d.DEPARTMENT_ID = e.DEPARTMENT_ID
    AND d.LOCATION_ID = l.LOCATION_ID
  GROUP BY d.DEPARTMENT_NAME, l.CITY;

原因：

因为select列表中的每个非聚合列都必须包含在

GROUP BY

子句中。此处非聚合列为

d.DEPARTMENT\u NAME，l.CITY

，因此

分组依据为
d.DEPARTMENT\u NAME，l.CITY

 SELECT d.DEPARTMENT_NAME, l.CITY, count(e.FIRST_NAME), avg(e.SALARY)
   FROM DEPARTMENTS d, LOCATIONS l, EMPLOYEES e
  WHERE d.DEPARTMENT_ID = e.DEPARTMENT_ID
    AND d.LOCATION_ID = l.LOCATION_ID
  GROUP BY d.DEPARTMENT_NAME, l.CITY;