Question

我想获取数据库中所有部门的平均分数，我有一个查询，它仅获取一个部门的平均分数，有没有办法我可以获取部门的名称和平均分数。假设我有2个部门（服务器和IT），服务器的平均值是该部门人员的所有分数之和除以部门总数。

这是我的查询，但这只是一个部门的平均值

SELECT SUM(RatingId)/(select COUNT(Id) from Employee where DepartmentId = 5) as Sums
FROM PerformanceReviewRatings pfr join
     Employee e
     on pfr.EmployeeId = e.Id join
     Department d
     on d.Id = e.DepartmentId
WHERE pfr.AppraisalId = 1009;

Answer 1

使用group by

SELECT e.DepartmentId, d.name, 
       SUM(RatingId)/COUNT(1) as Sums
  FROM PerformanceReviewRatings pfr
  JOIN Employee e
    ON pfr.EmployeeId = e.Id 
  JOIN Department d
    ON d.Id = e.DepartmentId
 WHERE pfr.AppraisalId = 1009
 GROUP BY e.DepartmentId, d.name

Answer 2

假设一名员工仅获得一个等级，则不需要子查询或对Department表的引用：

SELECT e.DepartmentId,
       SUM(RatingId)/COUNT(*) as average_rating
FROM Employee e LEFT JOIN
     PerformanceReviewRatings pfr
     ON pfr.EmployeeId = e.Id AND
        pfr.AppraisalId = 1009
GROUP BY e.DepartmentId;

如果您只希望获得具有评级的员工的平均值，而不是您的问题提出的答案（即将未评级的员工视为0，则：

SELECT e.DepartmentId, AVG(RatingId) as average_rating
FROM Employee e JOIN
     PerformanceReviewRatings pfr
     ON pfr.EmployeeId = e.Id
WHERE pfr.AppraisalId = 1009
GROUP BY e.DepartmentId

Answer 3

使用AVG（）函数。

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如何使用SQL获取部门的平均分数

3 个答案: