用sqlite按行平均
问题描述：
我正在使用sqlite数据库. 这些表是:
I'm working with a sqlite database. The tables are:
ID_TABLE POINTS_A_TABLE POINTS_B_TABLE
id number id_a points_a id_a points_a
-------------- ---------------- ----------------
smith 1 smith 11 ...
gordon 22 gordon 11
butch 3 butch 11
sparrow 25 sparrow
white 76 white 46
，依此类推.这些命令之后
and so on. After these commands
select id,
points_a_table.points_a, points_b_table.points_a, points_c_table.points_a, points_d_table.points_a
from id_table
left join points_a_table on points_a_table.id_a = id_table.id
left join points_b_table on points_b_table.id_a = id_table.id
left join points_c_table on points_c_table.id_a = id_table.id
left join points_d_table on points_d_table.id_a = id_table.id
group by id
我得到了这个结果，在每一行上我都有一个id和与该id关联的点.
I got this result, on each row I have the id and the points associated with the id.
现在，我想获得按行的平均点数，按平均降序. 我想要的是:
Now I'd like to get an average of points by row, sorted by average in descending order. What I want is:
sparrow| 56 [(44+68)/2]
white | 41 ([46+67+11)/3]
smith | 33 [(11+25+65)/3]
butch | 24 [(11+26+11)/3]
gordon | 11 [11/1]
我该怎么做? 谢谢.
答
如果将所有点表混在一起，则可以简单地计算每组的平均值:
If you smush together all point tables, you can then simply compute the average for each group:
SELECT id,
avg(points_a)
FROM (SELECT id_a AS id, points_a FROM points_a_table
UNION ALL
SELECT id_a AS id, points_a FROM points_b_table
UNION ALL
SELECT id_a AS id, points_a FROM points_c_table
UNION ALL
SELECT id_a AS id, points_a FROM points_d_table)
GROUP BY id
ORDER BY avg(points_a) DESC;