Transaction Facts: One Row Per Event

Transaction facts are the most common fact table type and the one most candidates get right. The grain is one row per discrete business event. Rows are inserted and never updated. This is the natural model for clicks, payments, orders, log entries, and any event stream. The Schema the Interviewer Expects The Trap: When the Interviewer Asks for Current State Transaction facts cannot answer 'what is the current state?' questions. They can tell you every event that happened, but not the net result of all those events at a point in time. This is the interview trap. The Follow-Up Trap