在 postgresql 中具有分组的嵌套聚合函数
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Nested aggregate functions with grouping in postgresql
提问by ferson2020
I'm trying to get an average of sums using nested aggregate functions and grouping. What I would want to do is:
我正在尝试使用嵌套的聚合函数和分组来获得总和的平均值。我想做的是：
SELECT AVG(SUM(x) GROUP BY y) WHERE ... GROUP BY ...;
That is, for each row returned, I want one of the fields to be an average of sums, where each sum is over the rows where y is the same.
也就是说，对于返回的每一行，我希望其中一个字段是总和的平均值，其中每个总和都在 y 相同的行上。
I would like to avoid subselects if possible.
如果可能，我想避免子选择。
回答by Gordon Linoff
You need a subquery:
你需要一个子查询：
select z, avg(sumval)
from (select y, z, sum(x) as sumval
from t
group by y, z
) t
group by z
