如何从 Postgresql 中的计算列中获取平均值？

Question

我有一个问题：

SELECT sum(column_1),
   sum(...) as sum_1,
   sum(...) as sum_2,
   sum(...) as sum_3
FROM table_1

如何从sum_1、sum_2、sum_3获取平均数据？如果我用下一种方式写一个查询：

SELECT sum(column_1),
   sum(...) as sum_1,
   sum(...) as sum_2,
   sum(...) as sum_3,
   avg(sum_1, sum_2, sum_3)
FROM table_1

我遇到一个错误：

[42703] ERROR: column "sum_1" does not exist

Answer 1

您似乎想要计算同一行上三列的平均值。如果是这样，则不需要 avg() （这是一个跨行操作的聚合函数）。相反，您可以使用常规算法：

SELECT *, (sum_1 + sum_2 + sum_3) / 3 as sum_average
FROM (
    SELECT sum(column_1), sum(...) as sum_1, sum(...) as sum_2,sum(...) as sum_3
    FROM table_1
) t

子查询不是严格必需的。您也可以重复 sum()，例如：

SELECT sum(column_1), sum(...) as sum_1, sum(...) as sum_2,sum(...) as sum_3,
    (sum(...) + sum(...) + sum(...)) / 3 as sum_average
FROM table_1

如何从 Postgresql 中的计算列中获取平均值？

How to get the average from computed columns in Postgresql?

sql

postgresql

average

sum

aggregate-functions