The Growth Rate Question in Disguise

Concepts covered: sqlLagLead

What 'prior period' means, and how to spot the question A period-over-period query computes a value (revenue, active users, signups) for each period, and pairs every row with the corresponding row from the prior period. The pairing rule defines what 'prior' means. For month-over-month, prior is the immediately previous calendar month. For year-over-year, prior is the same month one year ago. For week-over-week, prior is the previous seven-day window. The choice of pairing rule is a business decision; ask the interviewer which one they want before you write the query. Then, when you do start writing, say one sentence first: 'This is a period-over-period question. I will pre-aggregate to the period grain, then use LAG to get the prior period's value, then compute the growth rate as the diffe

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