在 MySQL 中平均某個列值

Question

我有這個表結構：

id | code | rating 
1  | 300  |   25
2  | 302  |   35
3  | 100  |   50
4  | 100  |   30
5  | 200  |   40
6  | 103  |   45

到目前為止，這是我的查詢：

SELECT 代碼，AVG(rating) FROM table GROUP BY 代碼；

我想平均所有代碼的評分大於 300。我嘗試在 SQL 查詢上設置 IF，但似乎不起作用。 也試過有兩個組 BY，但它不起作用。 我想達到這個結果：

code         |  AVG (rating)
300+ (alias) |  30
100          |  40
200          |  40
103          |  45

Answer 1

在group by用case when ：

select
    case when code >= 300 then '300+' else code end as code,
    avg(rating) as `AVG (rating)`
from yourtable
group by case when code >= 300 then 300 else code end
order by `AVG (rating)`

這是 SQLFiddle 中的演示。

注意：這將在 MySQL 中工作，但由於300+是字符串，因此更嚴格的方法應該首先將代碼轉換為varchar ：

select
    case when code >= 300 then '300+' else concat(code, '') end as code,
    avg(rating) as `AVG (rating)`
from yourtable
group by case when code >= 300 then '300+' else concat(code, '') end
order by `AVG (rating)`

Answer 2

SELECT CODE,AVG(rating) FROM
(
SELECT CASE WHEN code >= 300 THEN '300+' ELSE CODE END AS CODE, rating FROM table 
)Z
GROUP BY code;

你可以試試上面的代碼。

Answer 3

您可以使用case表達式將所有大於 300 的代碼組合在一起：

SELECT   CASE WHEN code >= 300 THEN '300+'
            ELSE CAST(code AS CHAR)
         END,
         AVG(rating) 
FROM     table 
GROUP BY CASE WHEN code >= 300 THEN '300+'
            ELSE CAST(code AS CHAR)
         END

Answer 4

根據上述問題中提到的描述，請嘗試執行以下 SQL 選擇查詢作為解決方案。

 select code,avg(rating) from table where code < 300 group by code  
 union 
 select code,avg(rating) from table where code >= 300