Module 1 · From question to model Lesson 3 of 15
A star schema in plain language
One fact table of events and a few dimension tables of descriptions. It sounds academic until the first time a single flat file cannot answer "sales by region by month" without duplicating rows.
Worked example
A flat file with the region name repeated in every sales row doubles every total the moment it is joined to a region table. Splitting region into its own table is what fixes the double count, and it is the single most common interview question in this area.
Your practice task
Split your dataset into one fact table and two dimension tables, then draw the relationships before building anything.
Do this before moving on. Reading a solution teaches the shape of it; typing it teaches you.
Key takeaway
One fact table of events and a few dimension tables of descriptions. It sounds academic until the first time a single flat file cannot answer "sales by region by month" without duplicating rows.
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