Consider the following set of normalized relations from a database used by a mobile service provide to keep track of its users and advertiser customers.
Assume that the mobile service provider has frequent need for the following information:
• List of users sorted by zip code
• Access to a specific client with the client's contact person's name, e-mail address, and phone number
• List of users sorted by interest area and within each interest area user's estimated intensity of interest
• List of users within a specific age range sorted by their category and within the category by zip code.
• Access to a specific user based on their e-mail address. Based on these needs, specify the types of indexes you would recommend for this situation. Justify your decisions based on the list of information needs above.