Question

I have a problem with a query:
I have a list of stores, each of these stores has members and there are various categories of membership (Bronze, silver, gold …)

The tables are: ‘shops’, ‘members’, ‘membership_cards’.

shops: id, name
members: id, shops_id, membership_id, first_name, last_name
membership_cards: id, description

I need to extract the count of members, grouped by membership of each stores. Can I do this without using a server side language?

The final result should be something like:

Store’s name, n°bronze members, n°silver_members, n°gold_members ….

Answer 1

Based on what you provided, you want a query like:

select shopid,
       sum(case when c.cardtype = 'Bronze' then 1 else 0 end) as Bronze,
       sum(case when c.cardtype = 'Silver' then 1 else 0 end) as Silver,
       sum(case when c.cardtype = 'Gold' then 1 else 0 end) as Gold
from shops s left outer join
     members m
     on s.shopid = m.shopid left outer join
     cards c
     on c.memberid = m.memberid
group by shopid

If you want to know the number of members, rather than of cards in each group (if members can have more than one card), then replace the sum() expression with:

count(case when c.cardtype = 'Bronze' then m.memberid end)