3. SQL for Data Preparation

Activity 3.01: Building a Sales Model Using SQL Techniques

Solution:

1. Open pgAdmin, connect to the sqlda database, and open the SQL query editor.
2. Use INNER JOIN to join the customers table to the sales table:

   FROM sales s
   JOIN customers c
   ON s.customer_id = c.customer_id

Note that the SQL in Steps 2, 3, and 4 is not complete SQL that you can run in pgAdmin. They are part of the FROM…JOIN clause on which the full SELECT statement will be built. They are created to guide you through the process of forming a complex dataset using JOIN. If you want to test the SQL, you can make it complete by adding SELECT * at the start.

3. Use INNER JOIN to join the products table to the sales table:

   FROM sales s
   JOIN customers c
   ON s.customer_id = c.customer_id
   JOIN products p
     ON s.product_id = p.product_id

4. Use LEFT JOIN to join the dealerships table (right table) to the sales table (left table):

   FROM sales s
   LEFT JOIN dealerships...