QUEL

SLIDE #15          RETRIEVING DATA BETWEEN SEVERAL RELATIONS

To retrieve data from several relations, we use the retrieve command,
in conjunction with the range and where commands.

For Example:          range of s is student 
                      range of c is course
                      range of g is grade
                      retrieve (s.name, c.teacher, g.grade)      
                      where s.name=g.name
                      and g.course_id=c.course_id

The where clause specifies that we want:

. student name in the student relation and grade relation to be identical
. course_id in the course relation and grade relation to be identical

We edit a file, called session7  to retrieve data from several relations.