总和减去最小值的平均值

发布于 2024-10-05 21:30:18 字数 851 浏览 4 评论 0原文

我有一个 SQL 语句，用于获取不同活动类型（家庭作业、测验等）的成绩，如果该类型的成绩下降到最低，则下降，否则保持不变。下面是错误以及 SQL 代码。

SELECT     Student.firstName, Student.lastName, 'Grades' =
           CASE 
              WHEN Grades.activityType = 'Homework' THEN
                CASE WHEN Policy.drop_hw = 1 THEN
                    (AVG(SUM(Grades.grade) - MIN(Grades.grade))) * (Policy.homework / 100)
                ELSE
                    (AVG(Grades.grade) * (Policy.homework / 100))
                END
            END,  Course.courseNum, Course.sectNum, Grades.activityType

FROM ...

以下是我收到的错误：

- Cannot perform an aggregate function on an expression containing an aggregate or a subquery.
- Column 'Policy.drop_hw' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

原文

I have an SQL statement that grabs the grades of different activity types (Homework, Quiz, etc), and if there's a drop lowest for that type, it drops, else, it remains. The errors are below as well as the SQL Code.

SELECT     Student.firstName, Student.lastName, 'Grades' =
           CASE 
              WHEN Grades.activityType = 'Homework' THEN
                CASE WHEN Policy.drop_hw = 1 THEN
                    (AVG(SUM(Grades.grade) - MIN(Grades.grade))) * (Policy.homework / 100)
                ELSE
                    (AVG(Grades.grade) * (Policy.homework / 100))
                END
            END,  Course.courseNum, Course.sectNum, Grades.activityType

FROM ...

Here are the errors I'm getting:

- Cannot perform an aggregate function on an expression containing an aggregate or a subquery.
- Column 'Policy.drop_hw' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

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宁愿没拥抱 2024-10-12 21:30:18

研究分析函数。（SO问题，Oracle 文档）。

像这样：

AVG(Grades.grade) OVER (PARTITION BY Grades.student_id) AS avg_of_grades

and：

(AVG(SUM(Grades.grade) - MIN(Grades.grade))) OVER (PARTITION BY Grades.student_id) AS avg_grades_with_drop

根据您的情况设置分区；我们无法判断，因为您在示例中省略了 FROM ... 。

然后，您可以在 CASE 语句内的任何计算中使用这些列别名。

Look into analytical functions. (SO question, Oracle documentation).

Something like this:

AVG(Grades.grade) OVER (PARTITION BY Grades.student_id) AS avg_of_grades

and:

(AVG(SUM(Grades.grade) - MIN(Grades.grade))) OVER (PARTITION BY Grades.student_id) AS avg_grades_with_drop

Set the partitioning with whatever makes sense in your case; we can't tell since you omitted the FROM ... in your example.

You can then use those column aliases in any calculations inside your CASE statement.

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夜巴黎 2024-10-12 21:30:18

如果您只需要放弃一个最低成绩（在平局的情况下）

SELECT  student_id, AVG(grade)
FROM    (
        SELECT  *, ROW_NUMBER() OVER (PARTITION BY student_id ORDER BY grade) rn
        FROM    my_tables
        )
WHERE   NOT (drop_hw = 1 AND rn = 1)
GROUP BY
        student_id

如果您需要放弃所有最低成绩：

SELECT  student_id, AVG(grade)
FROM    (
        SELECT  *, MIN(grade) OVER (PARTITION BY student_id) mingrade
        FROM    my_tables
        )
WHERE   NOT (drop_hw = 1 AND grade = mingrade)
GROUP BY
        student_id

If you only need to drop one lowest grade (in case of ties)

SELECT  student_id, AVG(grade)
FROM    (
        SELECT  *, ROW_NUMBER() OVER (PARTITION BY student_id ORDER BY grade) rn
        FROM    my_tables
        )
WHERE   NOT (drop_hw = 1 AND rn = 1)
GROUP BY
        student_id

If you need to drop all lowest grades:

SELECT  student_id, AVG(grade)
FROM    (
        SELECT  *, MIN(grade) OVER (PARTITION BY student_id) mingrade
        FROM    my_tables
        )
WHERE   NOT (drop_hw = 1 AND grade = mingrade)
GROUP BY
        student_id

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