SQL 选择 case when 和 group

Question

我有这张桌子

我想按年龄分组并统计性别类型

这个案例：

age <= 20 then 'Group <= 20'
age between 21-40 then 'Group 21-40'
age between 41-60 then 'Group 41-60'
age > 60 then 'Group > 60'

我已经尝试过这段代码，但出现错误：

%%sql
select customer_id, birthdate, extract('year' from current_date) - extract('year' from birthdate ) age
case when age <= 20 then 'Group <= 20'
when age between 21 and 40 then 'Group 21 - 40'
when age between 41 and 60 then 'Group 41 - 60'
else 'Group > 60' end gender
from dim_customer 
group by 1

有什么解决办法吗？提前致谢。

顺便说一句：我在 Python 中使用此代码

Answer 1

在 SELECT 中不使用别名列，但在 GROUP BY 和 ORDER BY 子句中使用。

-- PostgreSQL
SELECT t.*
     , CASE WHEN age <= 20 THEN 'Group <= 20'
            WHEN age BETWEEN 21 AND 40 THEN 'Group 21 - 40'
            WHEN age BETWEEN 41 AND 60 THEN 'Group 41 - 60'
            ELSE 'Group > 60' END gender 
FROM (SELECT customer_id, birthdate
           , extract('year' from current_date) - extract('year' from birthdate ) age
from dim_customer) t

请查看网址https://dbfiddle.uk/?rdbms=postgres_11&fiddle=38c6ba05adc779aed3063e490bcc6376

注意：使用 date_part('year', current_timestamp :: DATE) - date_part('year',birthdate) 进行年龄计算。

按组计算性别并使用别名

SELECT CASE WHEN age <= 20 THEN 'Group <= 20'
            WHEN age BETWEEN 21 AND 40 THEN 'Group 21 - 40'
            WHEN age BETWEEN 41 AND 60 THEN 'Group 41 - 60'
            ELSE 'Group > 60' END gender
        , COUNT(t.gender) count_gender
        , COUNT(CASE WHEN t.gender = 'M' THEN 1 END) gen_male
        , COUNT(CASE WHEN t.gender = 'F' THEN 1 END) gen_female
FROM (SELECT customer_id, birthdate, gender
           , extract('year' from current_date) - extract('year' from birthdate ) age
           , date_part('year', current_timestamp :: DATE) - date_part('year', birthdate) age1
from dim_customer) t
GROUP BY CASE WHEN age <= 20 THEN 'Group <= 20'
            WHEN age BETWEEN 21 AND 40 THEN 'Group 21 - 40'
            WHEN age BETWEEN 41 AND 60 THEN 'Group 41 - 60'
            ELSE 'Group > 60' END

请查看网址https://dbfiddle.uk/?rdbms=postgres_11&fiddle=ad8af9dd9b82ede20452377615ca7fde