How to I construct a SQL VIEW of “inventory” for all “stores” in same “zone”?

Question

I have a PHP/MySQL app that has the following tables:

STORE:
store_id(1), ...
store_id(2), ...
store_id(3), ...
store_id(4), ...
store_id(5), ...

ZONE:
zone_id(A), store_id(1)
zone_id(A), store_id(2)
zone_id(B), store_id(1)
zone_id(B), store_id(3)
zone_id(B), store_id(5)
zone_id(C), store_id(4)
zone_id(C), store_id(5)

INVENTORY:
inv_id, store_id, ...
...

As you can see, a store may be in more than one zone, but zone_id + store_id must be unique (ie, store may appear in a zone only once.)

Given only 'store_id', then:

How do I create a view of INVENTORY for all STOREs in same ZONE as the given 'store_id'?

Answer 1

Given a store_id (identified below as ? ), this query gives you all other stores that belong to the same zone(s):

select store_id
from zone z
where exists (
    select 1
    from zone z1
    where 
        z1.zone_id = z.zone_id
        and z1.store_id = ?
)

You can turn this to a subquery and use in to pull out the corresponding inventories:

select i.*
from inventory i
where i.store_id in (
    select store_id
    from zone z
    where exists (
        select 1
        from zone z1
        where 
            z1.zone_id = z.zone_id
            and z1.store_id = ?
    )   
)

Answer 2

I assume that you mean in the same zone s as the store.

Write a query to select the zone of the store:

SELECT zone_id 
FROM _ 
WHERE store_id = 'your_id'

We will use this as an inner query.

Write an outer query

CREATE VIEW _ AS 
SELECT _ 
FROM _ 
WHERE store_id IN (Inner query) AND store_id <> 'your_id

to get all the stores in the same zone.

I'll let you build on that outer query to do any joins and selections you need.