Context

At Instacart, many operational analyses in Caper Cart and fulfillment reporting require combining order-level data with shopper and retailer attributes. Interviewers ask this to check whether you understand how joins affect row counts, missing data, and downstream metrics.

Core question

Explain how you would join orders, shoppers, and retailers tables to support an analysis. In your answer, describe:

1. Which keys you would join on
2. When to use INNER JOIN versus LEFT JOIN
3. How you would avoid duplicate rows or inflated aggregates
4. What metrics you could compute after the join

Scope guidance

The interviewer is not looking for advanced SQL syntax here. They want a clear explanation of join logic, table relationships, common pitfalls, and how your join choice changes the business result.