无法使用 SQL 选择不同位置的平均分数

Posted 2023-02-25

【中文标题】无法使用 SQL 选择不同位置的平均分数

【英文标题】：Unable to select average scores for different locations using SQL

【发布时间】：2017-06-21 03:59:36

【问题描述】：

我正在尝试选择特定位置的平均分数进行比较 目的。使用语句

SELECT l.location_name AS "Location Of Store",
        AVG (f.score) AS "Average Score"
    FROM feedback AS f
    JOIN employee AS e
        ON f.qr_id = e.qr_id
    JOIN location AS l
        ON e.location_id = l.location_id
    WHERE e.company_id = '1'

results in

+ ----------------- + ------------- +
| Location of Store | Average Score |
+ ----------------- + ------------- +
| London            | 5.3333        |
+ ----------------- + ------------- +

如果我降低平均水平

SELECT l.location_name AS "Location Of Store",
        f.score AS "Average Score"
    FROM feedback AS f
    JOIN employee AS e
        ON f.qr_id = e.qr_id
    JOIN location AS l
        ON e.location_id = l.location_id
    WHERE e.company_id = '1'

Then the results I want to see however this isn't the average score

+ ----------------- + ------------- +
| Location of Store | Average Score |
+ ----------------- + ------------- +
| London            | 9             |
| Bedfordshire      | 2             |
| Buckinghamshire   | 5             |
+ ----------------- + ------------- +

可能错过了一些简单的东西，我不能指望它！

【参考方案1】：

看起来您只是缺少“分组依据”子句。另外，我认为您的第一个语句甚至不会编译正确？

试试这个：

SELECT l.location_nameAS "Location Of Store", AVG (f.score) AS "Average Score"
FROM feedbackAS f
JOIN employeeAS e
ON f.qr_id= e.qr_id
JOIN locationAS l
ON e.location_id = l.location_id
WHERE e.company_id = '1'
GROUP BY l.location_name

Group by 子句实际上是按不同字段中的值对聚合函数的结果进行分组。聚合函数如 min、max、count、avg、stddev 等。

【讨论】：

真不敢相信我错过了，今天花了太长时间看这个屏幕。 top语句求所有结果的平均值，如图5.5所示。