DBI202Xuất hiện trong 1 đề thi
Consider the two relations from our running movie database: Movies(title, year, length, genre, studioName, producerC#) MovieExec(name, address, cert#, netWorth) The producerC# component of each Movies tuple must also appear in the cert# component of some MovieExec tuple. How can we express this integrity constraint in relational algebra?
Các lựa chọn
A$\pi_{\text{producerC\#}}(\text{Movies}) = \pi_{\text{cert\#}}(\text{MovieExec})$
B$\pi_{\text{producerC\#}}(\text{Movies}) \subseteq \pi_{\text{cert\#}}(\text{MovieExec})$
C$\pi_{\text{cert\#}}(\text{MovieExec}) \subseteq \pi_{\text{producerC\#}}(\text{Movies})$
D$\pi_{\text{producerC\#}}(\text{Movies}) \ne \pi_{\text{cert\#}}(\text{MovieExec})$