Question

假设我在Postgres中有一个名为listings的表，如下所示：

id    neighborhood    bedrooms    price
1     downtown        0           256888
2     downtown        1           334000
3     riverview       1           505000
etc.

如何编写交叉表查询，将每间卧室的平均价格显示为列和邻域作为行？

查询的输出应该如下所示（数字组成，列是卧室）：

            0       1       2       3
riverton    250000  300000  350000  -
downtown    189000  325000  -       450000

Answer 1

首先使用聚合函数avg()计算平均值：

SELECT neighborhood, bedrooms, avg(price)
FROM   listings
GROUP  BY 1,2
ORDER  BY 1,2

然后按照相关答案中的详细说明将结果提供给crosstab()函数：

PostgreSQL Crosstab Query

Answer 2

在Postgres中构建数据透视表的最佳方法是Case语句。

select neighborhood,
round(avg((case when bedroom = 0 then price else 0 end)),2) as "0",
round(avg((case when bedroom = 1 then price else 0 end)),2) as "1",
round(avg((case when bedroom = 2 then price else 0 end)),2) as "2",
round(avg((case when bedroom = 3 then price else 0 end)),2) as "3",
from listings
group by neighborhood;

这是我的输出

NEIGHBORHOOD                  0          1          2          3
-------------------- ---------- ---------- ---------- ----------
downtown                      0     373.38     328.25     524.63
riverview                     0     256.83          0       1341
north                         0     199.15     507.85     986.31

Answer 3

另一种使用过滤器实现的解决方案：

SELECT neighborhood,
   avg(price) FILTER (WHERE bedrooms = 0) AS "0",
   avg(price) FILTER (WHERE bedrooms = 1) AS "1",
   avg(price) FILTER (WHERE bedrooms = 2) AS "2",
   avg(price) FILTER (WHERE bedrooms = 3) AS "3"
FROM listings
GROUP BY neighborhood;

使用PostgreSQL创建一个数据透视表

3 个答案: