# Question

In Chapter we saw how to represent many-to-many, many-to-one, one-tomany, and one-to-one relationship sets. Explain how primary keys help us to represent such relationship sets in the relational model.

## Answer to relevant Questions

Consider the relational database of Figure, where the primary keys are underlined. Give an expression in the relational algebra to express each of the following queries:a. Find the names of all employees who work for First ...Consider the relational database of Figure. Give a relational-algebra expression for each of the following queries:a. Find the company with the most employees.b. Find the company with the smallest payroll.c. Find those ...Let R = (A, B) and S = (A, C), and let r(R) and s(S) be relations. Using the special constant null, write tuple-relational-calculus expressions equivalent to each of the following: a. r 1 s b. r 1 s c. r 1 sLet R = (A, B) and S = (A, C), and let r(R) and s(S) be relations. Write an expression in SQL for each of the queries below: a. {< a > | ∃ b (< a, b >∈ r ∧ b = 17)} b. {< a, b, c > | < a, b >∈ r ...Write check conditions for the schema you defined in Exercise 4.14 to ensure that:a. Every employee works for a company located in the same city as the city in which the employee lives.b. No employee earns a salary higher ...Post your question

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