Data Scientist · Phone Screen · Multiple Types

DoorDash — Data Scientist ✅ Passed

Level: Unknown Level

Round: Phone Screen · Type: Multiple Types · Difficulty: 5/10 · Duration: 60 min · Interviewer: Neutral

Topics: SQL, Product Sense, Experimentation, Data Collection

Location: San Francisco, CA

Interview date: 2026-02-15

Summary

The SQL questions are standard ones I’ve seen before, specifically the 'Restaurant' problem.

When you practice these, you can’t just focus on getting the right output. You need to prepare for drill-down questions on the details. For example, be ready to explain exactly why you chose a specific line of code—like whether adding DISTINCT to a certain row actually changes the result or performance, and why.

For the 'Biker' product case, expect 4 to 5 follow-up questions covering different layers of the business:

1. Data Collection: How are we actually getting this data?
2. Challenges: What are the technical or real-world edge cases?
3. Pros & Cons: What are the trade-offs of this specific solution?
4. Experimentation: How would you design an A/B test to verify this?"

Details

What this means for your preparation:

The interviewer isn't just checking if you can code; they are checking if you have Product Sense and Engineering Rigor. Here is how to handle the specific layers mentioned:

The SQL "Details" (The DISTINCT example)

If you use DISTINCT, they might ask: "Is the data already unique because of the primary key? If so, why add the overhead of a sort operation?" * Tip: Only use DISTINCT if you can explain the specific duplicate scenario you are trying to prevent.

The Product Layers

When discussing the "Biker" (delivery rider), they want to see if you understand the Physical-to-Digital gap:

• Data Collection: Don't just say "we have a table." Say: "We collect GPS pings from the Biker's app every 10 seconds to calculate 'Wait Time' at the restaurant."
• Challenges: Mention "GPS drift" or "Bikers forgetting to mark an order as picked up."
• Experimentation: If the goal is to reduce Biker idle time, explain how you would split the test (e.g., Switchback Testing—alternating the algorithm every hour in a specific city—to avoid "interference" between bikers in the same area).