mysql - 仅当存在多个不等于 0 的值时，SQL 查询平均值才存在？

Question

如果特定 item_id 存在两个或多个非零值，我只想计算值的 AVG。如果不存在两个或多个非零值，我不想计算 AVG。

当前的 SQL 如下。也许应该先有一个 if 子句？...有什么想法吗？

SELECT AVG( days_since ) AS days_out
  FROM (
    SELECT days_since
    FROM user_123
    WHERE item_id = 645
AND days_since <> 0
ORDER BY id DESC
    LIMIT 5
  ) AS recent 

看起来 If 子句可能有效；

IF SELECT COUNT (*), item_id, days_since >= 2 
where days_since <>0, then perform AVG...

Answer 1

关于:

SELECT AVG(days_since) AS days_out
  FROM User_123
 WHERE Item_ID = 645
   AND Days_Since <> 0
HAVING COUNT(*) > 1

我不确定 ORDER BY 和 LIMIT 子句的用途，因此您必须调整答案以重新施加它们隐含的条件。

<小时/>

How to keep it working while reapplying Order By and Limit. These are used so that only the 5 most recent entries are used in the Average calculation.

SELECT AVG(days_since) AS days_out
  FROM (SELECT days_since
          FROM User_123
         WHERE Item_ID = 645
           AND Days_Since <> 0
         ORDER BY ID DESC
         LIMIT 5
       ) AS u
HAVING COUNT(*) > 1;