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