Should a SKU be associated to warehouse or supply table? This may be a trivial question for any of you experienced in supply chain models. The model I am building in PosgreSQL has 3 tables:
create table supply (
  id       serial primary key,
  barcode  varchar,
  title    varchar
  ...
);

create table warehouse (
  id     serial primary key,
  title  varchar,
  ...
);

create table warehouse_supply (
  id            serial primary key,
  warehouse_id  bigint not null,
  supply_id     bigint not null,
  ...
  foreign key (supply_id) references supply (id),
  foreign key (warehouse_id) references warehouse (id)
);

I was tempted to include an SKU (Stock Keeping Unit) column at table supply, but the very definition of SKU made me think it is a warehouse right to state their own SKU naming policy (this could occur with 3rd party warehouses).
Am I right? Should I include an sku varchar column at warehouse_supply instead of supply?
If the SKU is an attribute of a supply entity being located at a warehouse, then I would agree with your assessment to put it in the warehouse_supply table.
OTOH, if the company has decided that SKUs are the same regardless of the location, then it is an attribute of supply.