Chapter 16, Problem 9PE

Explanation of Solution

Explanation:

• The given expressions are,
  • A,Bγagg(C)(E1 ⋈ E2)
  • (Aγagg(C)(E1)) ⋈ E2
• The above two expressions are equivalent in the following situations,
  • The relation E₂ contains only the attributes A and B.
  • In relation R₂, there is no duplication as “A” is the primary key.
  • The aggregate output for first expression will be different from the output of second expression if duplicates are allowed...