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Tác giả Quentin Cappart
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Lecture d'algèbre relationnelle

Pour cette question, on va considérer ces relations de la base de données university :

  • \(\mathsf{course}(\underline{course\_id}, title, dept\_name, credits)\)
  • \(\mathsf{prereq}(\underline{course\_id},\underline{prereq\_id})\)
  • \(\mathsf{department}(\underline{dept\_name}, building, budget)\)
  • \(\mathsf{student}(\underline{ID}, name, dept\_name, tot\_credit)\)
  • \(\mathsf{instructor}(\underline{ID}, name, dept\_name, salary)\)
  • \(\mathsf{advisor}(\underline{s\_ID}, i\_ID)\)

Nous n'avons pas besoin de connaître les tuples de la table. Réferez vous au diagramme des schémas pour repérer les référencements via les clefs étrangères.

Indiquez l'énoncé correspondant aux requêtes suivantes.

Câu hỏi 1:

\(\pi_{ID}(student) - \pi_{s\_ID}(advisor)\)

Câu hỏi 2:

\(\pi_{dept\_name}(student) - \pi_{dept\_name}(department)\)

Câu hỏi 3:

\(|\pi_{dept\_name}(student \bowtie_{student.dept\_name=department.dept\_name} department)|\)

Câu hỏi 4:

\(\pi_{ID}(student \bowtie advisor)\)

Câu hỏi 5:

\(\pi_{course\_id}(course) - \pi_{course\_id}(prereq)\)

Câu hỏi 6:

\(\pi_{student.name}(\sigma_{student.ID=advisor.s\_ID \land advisor.i\_ID=instructor.ID}(student \times advisor \times instructor))\)

Câu hỏi 7:

\(\pi_{dept\_name}(department) - \pi_{dept\_name}(course)\)

Câu hỏi 8:

\(\pi_{ID,name}(student) - \pi_{student.ID,student.name}(student \bowtie advisor)\)

Câu hỏi 9:

\(|\pi_{i\_ID}(advisor)|\)

Câu hỏi 10:

\(\pi_{dept\_name}(student) \cap \pi_{dept\_name}(instructor)\)

Câu hỏi 11:

\(\pi_{student.ID}(\sigma_{student.dept\_name=instructor.dept\_name \land instructor.salary>90000}(student \times instructor))\)

Câu hỏi 12:

\(\pi_{ID}(student) - \pi_{student.ID}(\sigma_{student.dept\_name=instructor.dept\_name}(student \times instructor))\)

Câu hỏi 13:

\(\pi_{ID}(student) - \pi_{ID}(student \bowtie_{student.dept\_name=instructor.dept\_name} instructor)\)

Câu hỏi 14:

\(\pi_{dept\_name}(student) \subseteq \pi_{dept\_name}(department)\)

Câu hỏi 15:

\(\pi_{i\_ID}(advisor) - \pi_{ID}(instructor)\)

Câu hỏi 16:

\(|\pi_{dept\_name}(student \times instructor)|\)

Câu hỏi 17:

\(\pi_{dept\_name}(course) - \pi_{dept\_name}(student)\)

Câu hỏi 18:

\(\pi_{student.ID}(student) \cap \pi_{advisor.s\_ID}(advisor)\)

Câu hỏi 19:

\(\pi_{course\_id}(\sigma_{course.dept\_name=department.dept\_name}(course \times department))\)

Câu hỏi 20:

\(\pi_{dept\_name}(student \bowtie_{student.dept\_name=department.dept\_name} department) = \pi_{dept\_name}(student)\)