Yurttas/PL/DBL/postgres/F/01/PC/q18.sql

 1/*
 2REM
 3REM q18.sql
 4REM
 5REM Find the manufacturers who sell exactly three different
 6REM models of PC.
 7REM
 8*/
 9
10SELECT current_schema();
11SET search_path to "pc";
12
13SELECT P.maker
14FROM Product P, PC
15WHERE P.model=PC.model
16GROUP BY P.maker
17HAVING COUNT(DISTINCT PC.model)=3;