Lista del curso Inicia sesión

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Autor(es) Quentin Cappart
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Inicia sesión

Inicia sesión

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.

Pregunta 1:

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

Pregunta 2:

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

Pregunta 3:

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

Pregunta 4:

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

Pregunta 5:

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

Pregunta 6:

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

Pregunta 7:

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

Pregunta 8:

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

Pregunta 9:

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

Pregunta 10:

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

Pregunta 11:

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

Pregunta 12:

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

Pregunta 13:

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

Pregunta 14:

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

Pregunta 15:

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

Pregunta 16:

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

Pregunta 17:

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

Pregunta 18:

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

Pregunta 19:

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

Pregunta 20:

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