Given the usual suppliers-and-parts database, what is the value of the expression S join Sp join P? What is the corresponding predicate? Warning; there is a trap here.
Answer to relevant QuestionsLet r be a relation of degree n. How many different projections of r are there?Given that intersect is a special case of join, why do not both operators give the same result when applied to no relation at all?Get project numbers for projects supplied by at least one supplier not in the same city.Get project numbers for projects not supplied with any red part by any London supplier.Suppose that every row in the matrix A of a linear program Ax ≤ b corresponds to a difference constraint, a single-variable constraint of the form xi ≤ bk, or a single-variable constraint of the form -xi ≤ ...
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