employee (personname, street, city) works (persor_nате, соmpany-лате, salary) сompany (compапy-naте, сity) Figure 2.17 Employee database.

(FROM DATABASE SYSTEMS, 13TH ED.) Problem 15. Use a query to compute the total of all purchases, the number of purchases, and the average purchase amount made by each customer. Your output values must match those shown in Figure P7.15. Sort the results by customer code.

I am having problems finding the answers to this assignment ( Lab 5:2 StayWell Student Accommodation).  Please explain how to solve (tasks 5-8) and the sql code needed to get the desired results.   Task 5 - Repeat task four, but this time use the EXISTS operator in your query. Task 6 - List the property IDs of any pair of properties that have the same number of bedrooms.  For example, one pair would be ID 2 and property ID 6, because they both have 4 bedrooms.  The first property ID listed should be the major sort key and the second property ID should be the minor sort key. Task 7 - List the sq footage, owner number, owner last name and owner first name for each property managed by the StayWell-Columbia City Office. Task 8 - Repeat task 7, but this time include only those properties with three bedrooms.

Consider the following expressions, which use the result of a relational algebra operation as the input to another operation. For each expression, explain in words what the expression does. a. year 2009 (takes) ▷ student b. year 2009 (takes ▷ student) C. ID.name, course_id (student takes)