- #1
AntoineCompagnie
- 12
- 0
Let's assume that the Congress library has a database with the
following pattern (the primary keys are in bold)
Borrowing(People, Book, DateBorrowing, ExpectedReturnDate,
EffectiveReturnDate) Lateness(People, Book, DateBorrowing,LatenessFee)
Who are those that have never return a book late in relational algebra? In relational calculus?
I think that in relational algebra, they are: $$\Pi_{People}(Borrowing)\div \Pi_{People}(Delayness)$$ But I'm not sure!
And I definately don't know how to turn out that in relational calculus...
$$\{t.People|Delayness(t)\wedge\dots$$
Have you any hint?
following pattern (the primary keys are in bold)
Borrowing(People, Book, DateBorrowing, ExpectedReturnDate,
EffectiveReturnDate) Lateness(People, Book, DateBorrowing,LatenessFee)
Who are those that have never return a book late in relational algebra? In relational calculus?
I think that in relational algebra, they are: $$\Pi_{People}(Borrowing)\div \Pi_{People}(Delayness)$$ But I'm not sure!
And I definately don't know how to turn out that in relational calculus...
$$\{t.People|Delayness(t)\wedge\dots$$
Have you any hint?