根据特定值创建新列另一列

Question

Let say I have this kind of column

create table exercise (cust_id varchar, policy_id varchar, end_date date, flag varchar);   
insert into exercise (cust_id, policy_id, end_date, flag)
values
('1', 'a1', '2022-10-12', 'inactive'),
('1', 'a2', '2022-10-20', 'inactive'),
('1', 'a2', '2023-05-15', 'active'),
('2', 'a3', '2022-12-12', 'inactive')
('3', 'a3', '2022-09-18', 'inactive')
('3', 'a1', '2023-12-22', 'active')

from that column, we know that 3 customers (1, 2, 3) with 3 products(a1, a2, a3)
Is there any way to make new column,
if the customer have flag 'active' and 'inactive' then it called 'good',
but if the customer only have flag 'inactive' then it called 'bad'

so the output will be look like this, how the logic???

cust_id	policy_id	end_date	flag	credit
1	a1	2022-10-12	inactive	good
1	a2	2022-10-20	inactive	good
1	a2	2023-05-15	active	good
2	a3	2022-12-12	inactive	bad
3	a3	2022-09-18	inactive	good
3	a1	2023-12-22	active	good

Answer 1

We can use COUNT() here as a window function, along with conditional aggregation:

SELECT cust_id, policy_id, end_date, flag,
       CASE WHEN COUNT(CASE WHEN flag = 'active' THEN 1 END)
                     OVER (PARTITION BY cust_id) > 0
            THEN 'good' ELSE 'bad' END AS credit
FROM exercise
ORDER BY cust_id, end_date;

Answer 2

Try this :

SELECT *
      ,CASE WHEN MAX(CASE WHEN flag = 'inactive' THEN 1 END) OVER (PARTITION BY cust_id) = 1 AND MAX(CASE WHEN flag = 'active' THEN 1 END) OVER (PARTITION BY cust_id) = 1 THEN 'good' ELSE 'bad' END
FROM exercise 

Answer 3

we can use inner join as follows:

This one take on consideration if the last order is active or not.

Example if the last order of a customer is inactive he should be considered as bad customer:

SELECT *, CASE WHEN s.flag = 'active' THEN 'good' ELSE 'bad' END as credit
FROM exercise t
join (
  SELECT t.cust_id, t.flag
  FROM (
      select cust_id, max(end_date) as max_date
      from exercise
      group by cust_id
  ) r
  INNER JOIN exercise t
  ON t.cust_id = r.cust_id AND t.end_date = r.max_date
) as s on s.cust_id = t.cust_id

check it here: https://dbfiddle.uk/j0TtG62a