Question

SDS operates stores in the following cities: Melbourne, Ballarat, Geelong, Sydney, Newcastle, Brisbane, Adelaide and Perth. Stores are referenced by store number. SDS also keeps store name, street, city, state, postcode, telephone, and manager's details. Each store is assigned a supervising store where major customer complaints are referred, training is conducted, and server applications and help desk functions are located. The supervising store currently supervises stores within its own state boundaries but this is not necessarily going to continue in the future.

When a customer rings with a complaint, details of the complaint are to be recorded. The details include the date the complaint was made, the employee id of the person recording the complaint, the customers first name, last name, street address, town, state, postcode and phone numbers. A customer may provide the employee taking the call with more than one type of phone number and include mobile, fax, home and office numbers. A complaint may be one of three different types. It may be related to the store, one or more employees or product(s) of the store. If a complaint is about the store a short description of the complaint is recorded and it is referred to the manager. If the complaint is about employees of the store, the ID(s) of the employees involved in the complaint is recorded, along with a short description of the problem. If the complaint is about products, the product id, the number of items and a short description are recorded. A customer may be involved in a number of complaints. Currently, complaints are provided with individual identification numbers.   Once a complaint has been resolved, the date that the complaint was closed is recorded.

Whilst the complaint is open all contact with the customer is recorded. Details of the date, time, the employee making contact, the type of contact (phone, fax, email or personal visit) and a short description of the contact are all recorded.

If the complaint is about a product, a replacement is normally provided. The store likes to keep track of all of the products replaced and the date the items were sent to the customer.

The store would also like you to interface your database with its products table in its inventory database. The products table has fields including ProductId, ProductName, ProductDescription, ProductUnitCost.

You are required to design (using an E-R diagram) an entity-relationship model of the problem, convert the model into a relational model, assess the normal form of each schema and write SQL queries that will answer the following queries.

1. An alphabetically sorted list of all customers who have made a complaint. Only customer number and name are required.
2. A more complete customer list sorted by customer id. It should contain customer id, name, address and all available phone numbers.

3. The date on which the most recent complaint has been made. The date itself will suffice.
4. A list of all complaints still open. Displaying complaint number will be sufficient.
5. A list of all complaints sorted by the type of the complaint. Displaying the complaint identification number, the customer id, the date the complaint was made, and the type of complaint will be sufficient.
6. A list of all products involved in customer complaints. Display the product id and name, sort this using the product name.
7. A total of the cost price of all products replaced. Displaying the total amount will be sufficient.
8. A list of all customers with more than 4 complaints. The customer id and name should be displayed.
9. A list showing the total number of complaints made about employees in each department. Displaying the department id and the total number of complaints is sufficient.
10. A customer list for all complaints still open that shows when the customer was last contacted. The customer id, name, last date of contact and type should be displayed, the list should be listed in descending date order.

Answer 1

Below is the ER-diagram

Below is the Relational Model

All the above tables are in 3NF form.

SQL queries (working in SQL server) for above requirements :
An alphabetically sorted list of all customers who have made a complaint. Only customer number and name are required.
select customerId, CONCAT(firstName, " ", lastname) as name
from CUSTOMER
where customerId in (select distinct(customerId) from COMPLAINT)
order by CONCAT(first, " ", lastname);

A more complete customer list sorted by customer id. It should contain customer id, name, address and all available phone numbers.

select b.cutomerId,
CONCAT(b.firstName, " ", b.lastname) as name,
CONCAT(streetAddress, " ", town, " ", state, " ', postCode) as address,
(select STRING_AGG([contact], ', ') from CUSTOMER_CONTACT a where a.customerId = b.customerId) as contact
from CUSTOMER b
where b.customerId (select distinct(customerId) from COMPLAINT)
order by b.customerId

1. The date on which the most recent complaint has been made. The date itself will suffice.
   select max(openingDate) from COMPLAINT;
2. A list of all complaints still open. Displaying complaint number will be sufficient.
   select identifier from COMPLAINT where closeDate is null;
3. A list of all complaints sorted by the type of the complaint. Displaying the complaint identification number, the customer id, the date the complaint was made, and the type of complaint will be sufficient.
   select identifier, customerId, openingDate, type
   from COMPLAINT
   order by type.
4. A list of all products involved in customer complaints. Display the product id and name, sort this using the product name.
   select productId, name from PRODUCT
   where productId in (select distinct(productId) from PRODUCT_COMPLAINT)
   order by name;
5. A total of the cost price of all products replaced. Displaying the total amount will be sufficient.
   select sum(cost) from (
   select a.itemCount *  b.unitCost as cost
   from PRODUCT_COMPLAINT a, PRODUCT b
   where a.productId = b.productId and a.replacementDate < SYSDATE)
6. A list of all customers with more than 4 complaints. The customer id and name should be displayed.
   select customerId, CONCAT(firstName, " ", lastName) as name
   from CUSTOMER
   where customerId in (select customerId from COMPLAINT group by customerId having count(*)>4)
7. A list showing the total number of complaints made about employees in each department. Displaying the department id and the total number of complaints is sufficient.
   select a.department, count(*)
   from EMPLOYEE a, EMPLOYEE_COMPLAINT b
   where a.employeeId=b.employeeId
   group by a.department
8. A customer list for all complaints still open that shows when the customer was last contacted. The customer id, name, last date of contact and type should be displayed, the list should be listed in descending date order.
   select a.customerId, concat(b.firstName, " ", b.lastName) as name, a.lastContactDate, a.contactTypeUsed
   from COMPLAINT a, CUSTOMER b
   where a.customerId=b.customerId
   order by a.lastContactDate desc

Have a nice day :)