與多個BETWEEN MySQL查詢總是NULL

Question

也許我在這裏很明顯缺少這個，但爲什麼這個查詢總是NULL？

SELECT ROUND(AVG(`viewer_count`),0) AS avg_viewer FROM `table` 
WHERE 
(id BETWEEN 1 AND 8) 
AND 
(id BETWEEN 26 AND 32) 

是不是有可能得到這樣的多個範圍的平均值？

Answer 1

既然是不可能的id爲1和8之間，在26和32之間的同時，該查詢返回NULL作爲沒有行被匹配。如果您使用OR作爲註釋中建議的squemeamish，您將獲得兩個範圍內的平均值。

Answer 2

SELECT ROUND(AVG(CASE WHEN id BETWEEN 1 AND 8 THEN `viewer_count` END),0) AS avg_viewer1_8 
    , ROUND(AVG(CASE WHEN id BETWEEN 26 AND 32 THEN `viewer_count` END),0) AS avg_viewer26_32 
FROM `table`