Question

(I’m having a hard time even explaining this question)

I have 5 Tables, A, AZ, Z, BZ, B.

AZ represents a Many-to-Many relationship between A and Z.
BZ represents a Many-to-Many relationship between B and Z.

I would like a result set that is A B where B is linked to the full set of Z for a given A.

So, let’s say that Z is a Tag table and contains:

Tag1
Tag2
Tag3

A is an Object Table and contains:

ObjectA
ObjectB
ObjectC

B is a Widget Table and contains:

WidgetX
WidgetY
WidgetZ

AZ contains:

ObjectA  Tag1
ObjectA  Tag2
ObjectB  Tag3
ObjectC  Tag2
ObjectC  Tag3

BZ contains:

WidgetX  Tag1
WidgetX  Tag2
WidgetY  Tag2
WidgetY  Tag3
WidgetZ  Tag3

I want my result set to be:

ObjectA  WidgetX
ObjectB  WidgetY
ObjectB  WidgetZ
ObjectC  WidgetY

Is this doable in a query, or should I pull back some intermediate sets of data and iterate in code?

Answer 1

Okay, major edit to rejigger this based on your feedback. It’s a little kludgy, but here you go:

select distinct
    x.aid,
    x.bid
from
    (select
        az.aid,
        bz.bid,
        (select COUNT(1) from az az1 where az1.aid = az.aid) as acount,
        (select COUNT(1) from bz bz1 where bz1.zid in (select zid from az az1 where az1.aid = az.aid) and bz1.bid = bz.bid) as bcount
    from
        az
        inner join bz on
            az.zid = bz.zid
    ) x
where
    x.acount = x.bcount

It uses nasty subqueries to get the right counts, and then limits our rowset based on your criteria.