Defining Grain: One Row Represents What?

Your grain statement answer: 'The grain is a contract. Every row represents exactly one instance of X. If I can write a GROUP BY on the grain columns and get COUNT(*) > 1 for any group, the grain is violated.' Say this, then immediately write the validation query. The interviewer is checking whether you can enforce grain, not just define it. How Interviewers Grade Your Grain Statement Watch the progression from vague to interview-grade: The jump from 'good' to 'strong hire' is acknowledging that a line item can have multiple lifecycle events. The jump from 'strong hire' to 'senior+' is naming the enforcement mechanism, not just the concept. The Validation Move That Signals Production Experience The Follow-Up Trap Once you state a grain, the interviewer will probe it. They will introduce a