我只是想问是否有人可以帮助我理解这个查询的实际作用?
select location, address
from warehouse D
where not exists
( select * from product P, supplier S
where P.supplier_no = S.supplier_no
and S.name = 'Azure Supplies'
and not exists
( select *
from stock S
where P.product_no = S.product_no
and D.warehouse_no = S.warehouse_no ) ) ;