Case study 1: Product likes for an e-commerce site. An online store that sells hundreds of thousands of items a day wants customers to like or dislike products. Its relational design slows down as the likes table grows. You choose the right database, explain why, and design the schema with partition, clustering and composite keys so the site can quickly get a user's details, a product's details, all products a user liked and all users who liked a product.
Case study 2: Banking click logs. A global bank's MySQL storage can't keep up with its transaction and click logs. You redesign the system, migrate the old data and build a schema that returns daily counts, such as clicks on the deal-of-the-day page by device type or clicks on the home page by browser.
Case study 3: Customer help desk. You build a help desk table keyed by customer ID, ticket ID and action time, with the latest change shown first. You create the table, store the latest timestamp on every insert, view the data with CQL and query tickets within a time range.
Case study 4: Hotel booking. You model room availability for two hotels, bulk load a month of data from a CSV file, query by hotel and room, sort by date and write a user-defined function (UDF) that shows whether a room is available.
