Yurttas/PL/DBL/oracle/F/01/PC/q11.sql

 1REM
 2REM q11.sql
 3REM
 4REM Find the average hard disk size of a PC for all those
 5REM manufacturers that make printers.
 6REM
 7
 8SELECT P.maker, AVG(hd)
 9FROM Product P, PC
10WHERE P.model=PC.model
11  AND P.maker IN (SELECT P.maker
12                  FROM Product P, Printer R
13                  WHERE P.model=R.model)
14GROUP BY P.maker;