过滤使用 CASE Postgresql 创建的列

Question

I have a table below:

id int
user_id int
created_at datetime
status varchar
type varchar

and I am trying to answer the question "Write a query that returns the user ID of all users that have created at least one 'Refinance' submission and at least one 'InSchool' submission."

I figured out how this will be done:

select
    a.user_id
from
    (select
        user_id,
        sum(
            case
                when type='Refinance' then 1 else 0 end) as "Refinancecount",
        sum(
            case
                when type='InSchool' then 1 else 0 end) as "Inschoolcount"
    from
        loans
    group by 1) as a
where a.Refinancecount>=1 and a.Inschoolcount>=1

When I run only the inner query, everything is fine. I am getting 3 columns but when I run the whole query it says column Refinancecount doesn't found. I looked on internet and found when I am aliasing my case columns then I should't wrap them in double quotes and the query worked fine using this suggestion. But I read more about creating columns using CASE in postgre, and found people do wrap column names in double quotes (I have attached an example screenshot) . Then why my query doesn't work this way.

Answer 1

You should quote those fields in the where clause. Try:

where "Refinancecount" >= 1 and "Inschoolcount" >= 1

By the way, you can write this query without inner query, by using having clause:

select
        user_id
from
        loans
group by 1
having sum(case when type='Refinance' then 1 else 0 end) >=1 and sum(case when type='InSchool' then 1 else 0 end) >= 1

Answer 2

Yea it's said column Refinancecount doesn't found because you need to use quote where a."Refinancecount">=1 and a."Inschoolcount">=1 . If you name your column as "Inschoolcount" you need to refer to it with the "" otherwise a.Refinancecount will be converted to a.refinancecount

Answer 3

Why not make it simple like this

 select
    user_id
     from
    loans
   group by user_id having
   sum(
        case
            when type in ('Refinance', 
             'InSchool') then 1 else 0 end >=2) 

Answer 4

SELECT DISTINCT l1.user_id

from 

loans l1

join

loans l2

where

l1.type = 'Refinance'

and

l2.type = 'InSchool'

;