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Consider a database with the following three relations:

  • CREDITS (STUDENT; COURSE)
  • OFFERS (TEACHER; COURSE)
  • BELONGS (TEACHER; DEPARTMENT)


Given below is a code in query language QUEL. Describe in one English sentence the query posed by the given QUEL program.

 

range of s is CREDITS
range of t is OFFERS
retrieve into LIST 1 (1=s. STUDENT)
where s.COURSE=t.COURSE and
t.TEACHER="Dr.X"
retrieve into LIST 2 (1=s.STUDENT)
where s.COURSE =t.COURSE and
t.TEACHER ="Dr.Y"
retrieve into LIST3 (1=STUDENT)
where s.course =t.COURSE and
t.TEACHER ="Dr.Z"
range to e1 is LIST1
range of e2 is LIST2
range of e3 is LIST3
retrieve(E1.I)
where e1.I=e2.I and
where e1.I=e3.I
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