Mysql group_concat with in() function - mysql

Question

i'm trying to use group concat with in function on mysql, it didn't give me any syntax error but i'm not sure its working.
i'm trying to do something like that:
select
case
when weekday(ps.date) in (group_concat(vd.valid_days)) then ps.date
when weekday(ps.date+1) in (group_concat(vd.valid_days)) then DATE_ADD(ps.date, INTERVAL 1 DAY)
when weekday(ps.date+2) in (group_concat(vd.valid_days)) then DATE_ADD(ps.date, INTERVAL 2 DAY)
when weekday(ps.date+3) in (group_concat(vd.valid_days)) then DATE_ADD(ps.date, INTERVAL 3 DAY)
when weekday(ps.date+4) in (group_concat(vd.valid_days)) then DATE_ADD(ps.date, INTERVAL 4 DAY)
when weekday(ps.date+5) in (group_concat(vd.valid_days)) then DATE_ADD(ps.date, INTERVAL 5 DAY)
end as valid_date
from
purchase_shopping ps
left join
purchase_region pr on pr.id = ps.idfk_region
left join
valid_weeks_days vd on vd.idfk_region = pr.id
group by ps.id
what i need basically is to return a valid date if certain day is inside a group concat from a left join. I don't know if my logic is wrong or it does not work.
Obs: The group concat function return something like that: (1,2,5), so it's supposed to work with in() function.
Sample with reworked code data:
ps.date = 2018-10-17
weekday(ps.date) = 2
group_concat(vd.valid_days) = (1,4)
then valid_date will be 2018-10-19

Answer 1

Perhaps you simply wants :
select (case when uc.id is not null then 'It has items' end)
from shopping_cart sc left join
user_cart uc
on uc.id = sc.idfk_cart;

Answer 2

You cannot use result of group_concat in same query so you have to use a subquery
select
case
when weekday(date) in valid_days then date
when weekday(date+1) in valid_days then DATE_ADD(date, INTERVAL 1 DAY)
when weekday(date+2) in valid_days then DATE_ADD(date, INTERVAL 2 DAY)
when weekday(date+3) in valid_days then DATE_ADD(date, INTERVAL 3 DAY)
when weekday(date+4) in valid_days then DATE_ADD(date, INTERVAL 4 DAY)
when weekday(date+5) in valid_days then DATE_ADD(date, INTERVAL 5 DAY)
end as valid_date
from (
select ps.date, (group_concat(vd.valid_days)) as valid_days
from
purchase_shopping ps
left join
purchase_region pr on pr.id = ps.idfk_region
left join
valid_weeks_days vd on vd.idfk_region = pr.id
group by ps.id
) as sub_query