Question

Here is my schema:

Suppliers(sid: integer, sname: string, address string)

Parts(pid: integer, pname: string, color: string)

Catalog(sid: integer, pid: integer, cost: real)

bold indicates primary key.

I want to write a query to find all suppliers who supply every part. Here are two queries I have already:

-- get all parts for a given supplier
SELECT Parts.pid
FROM Suppliers
JOIN Catalog ON Catalog.sid = Suppliers.sid
JOIN Parts ON Parts.pid = Catalog.pid
WHERE Suppliers.sid = 4;

-- gets all parts that exist
SELECT Parts.pid
FROM Parts

What I want to do, in imperative terms, is something like this:

Define result set
Foreach Supplier:
    If the list of parts produced by a supplier 
    is equal to the total list of parts, add this supplier to the result set
Return result set

How can I translate this into MySQL?

Answer 1

Use:

SELECT s.*
  FROM SUPPLIER s
  JOIN (SELECT c.sid,
               COUNT(c.pid) AS num_parts
          FROM CATALOG c
      GROUP BY c.sid) x ON x.sid = s.sid
  JOIN (SELECT COUNT(*) AS total_parts
          FROM PARTS) y ON y.total_parts = x.num_parts