adding CHECK to impose constraints on more than one table

Question

I want to modify the following DDL to add CHECK constraints so that the manager of a store works at the same store and a store supplies all the products if its type is \'local\'

Answer 1

You can do this by changing your primary key in works_at, then adding unique constraints to ensure the uniqueness. This will be better than using check constraints:

CREATE TABLE works_at(
  employee_number CHAR(5),
  store_code CHAR(5),
  PRIMARY KEY(employee_number, store_code),
  FOREIGN KEY(employee_number) REFERENCES employee,
  FOREIGN KEY(store_code) REFERENCES store,
  CONSTRAINT UQ_Works_at_employee_number UNIQUE NONCLUSTERED(employee_number) -- ENSURES EMPLOYEE CAN ONLY WORK AT ONE STORE
  )

Then your manages table can reference works_at to ensure they manage the store they work at:

CREATE TABLE manages(
  employee_number CHAR(5),
  store_code CHAR(5),
  PRIMARY KEY(store_code),
  FOREIGN KEY(employee_number, store_code) REFERENCES works_at (employee_number, store_code)
  )

With regard to your second part, I don't see a way of enforcing the fact that stocks must contain all stores and all products, and this also seems kind of pointless, you are essentially asking for a table that is just a cross join of two other tables.