按其他（日期）列分组的一列复杂的 PostgreSQL 平均值

Question

这是我的数据库表的简化版本。

id	firstregistration	km
1	2017-03-24	234
2	2019-10-08	3456
3	2020-02-07	2454
4	2019-11-28	7686
5	2019-01-18	4564

该表包含汽车数据，例如：首次注册日期、里程、价格、车型...

我的目标是构建查询以从此数据库表中获取分析指标。我的最终目标应该是这样的：

我需要使用首次注册日期来构建年龄组，并据此提取其他数据。

目前我已经解决了第一列和第二列。 SQL 查询如下所示：

SELECT SUM(CASE WHEN date_part('year', age(firstregistration))<1 THEN 1 ELSE 0 END) AS "0-1",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 1 AND 2 THEN 1 ELSE 0 END) AS "1-2",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 2 AND 3 THEN 1 ELSE 0 END) AS "2-3",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 3 AND 4 THEN 1 ELSE 0 END) AS "3-4",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 4 AND 5 THEN 1 ELSE 0 END) AS "4-5",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 5 AND 6 THEN 1 ELSE 0 END) AS "5-6",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 6 AND 7 THEN 1 ELSE 0 END) AS "6-7",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 7 AND 8 THEN 1 ELSE 0 END) AS "7-8",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 8 AND 9 THEN 1 ELSE 0 END) AS "8-9",
    SUM(CASE WHEN date_part('year', age(firstregistration)) BETWEEN 8 AND 9 THEN 1 ELSE 0 END) AS "9-10",
    SUM(CASE WHEN date_part('year', age(firstregistration)) >= 10 THEN 1 ELSE 0 END) AS ">=10" FROM car_table

为此，我得到如下所示的输出：

这个结果很好，它解决了第一张图片上图表的前两列。现在我无法按这些组添加平均公里数据。

有谁知道如何轻松实现它？ 需要补充的重要一点是，平均 KM 查询不需要成为我的第一个查询的一部分。将此作为附加查询就足够了。谢谢。

Answer 1

我认为你可以在一个查询中得到结果。

SELECT  age , COUNT(age) as NroCars , AVG(km) , AVG(price) FROM (
     SELECT  date_part('year', age(firstregistration)) as age,
             km ,
             price
     FROM TABLE 
) temp_table
GROUP BY age