[英]AVG on same column by values in another column single sql query
I want to find AVG on same column by values in different column single sql query. 我想通过不同列单个sql查询中的值在同一列上找到AVG。
table - question_rating
review_id
question_id
rating
I want to find avg of group of questions as 我想查找一组问题的平均值
Desired output- 期望的输出
qustion_id rating
-------------------------
g1 4.4
g2 3.7
g3 5.6
g1 is group of questions (1,3) g2 is group of questions (2,6) g3 is group of questions (7,8) ....g8 g1是一组问题(1,3)g2是一组问题(2,6)g3是一组问题(7,8).... g8
pseudo code- 伪代码
select (if(qustion=1 and question=3) as g1,
if(qustion=2 and question=6) as g2), ..
)avg(rating of respective group) from question_rating
I know it can be done by taking query separately but I want to know by single query. 我知道可以通过单独进行查询来完成,但是我想通过单个查询来知道。
Or any easy way to find such output by php,etc. 或通过php等找到此类输出的任何简便方法。
You should make a table question_groups
您应该创建一个表
question_groups
question_id group_id
q1 g1
q2 g2
q3 g1
q4 g3
q5 g3
q6 g2
And the select will be 选择将是
select group_id, avg(rating)
from question_rating a
join question_groups b on (a.question_id= b.question_id)
group by group_id
SELECT
CASE question_id
WHEN 1 THEN 'g1'
WHEN 3 THEN 'g1'
WHEN 2 THEN 'g2'
WHEN 4 THEN 'g2'
ELSE 'others' END AS qGroup,
AVG(rating) AS AvgRating
FROM question_rating
GROUP BY
CASE question_id
WHEN 1 THEN 'g1'
WHEN 3 THEN 'g1'
WHEN 2 THEN 'g2'
WHEN 4 THEN 'g2'
ELSE 'others' END
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