In the “Dimensional Modeling - Star Schema” Video, Joe asked a question to write a SQL query for the 3NF setup for the following question “total sales amount for each productLine in USA”. In the answer, he suggests to join “products” with “productlines” table. Do we need this join as the column, “productLine” is already available in the “products” table? Please see the attached screen shot.
In the products table, the column productline is a foreign key. If you want any details about a product line, its name/text description , for example, you must join using that key to the productlines table. If you don’t have that, you could sum, group, or order the report by the productline but you couldn’t tell what they were.
I haven’t taken the class so can’t refer you to a place in the lectures where this is explained. That’s just standard 3NF design and use.