Coinbase·Data Scientist·Technical Phone Screen
Jul 2026
SQL-heavy technical screen for a DS role at Coinbase. Three questions, all back-to-back, all on the same invented schema. No behavioral stuff at all which surprised me, just pure query writing under time pressure.
- Given a users table and a transactions table, write SQL to compute adoption rate and transaction rate per region for August 2025. Adoption rate is the share of users in that region who adopted in August, transaction rate is the share who made at least one transaction in August.
- For each user, calculate the number of days between their adoption date and their first transaction. Only include users where adopted_at is not null and the first transaction happened after adoption. Then write a second query returning the p10, p50, and p90 of that value.
- Define a cross-region sale as any transaction where the transaction region differs from the user's earliest-ever transaction region. Write a query that returns all August 2025 transactions with a flag indicating whether each is a cross-region sale, plus the user's first transaction region.
“Took me longer than it should have to realize I needed to keep all users in the denominator, not just the ones with activity.” The rest of the author's notes on Data Scientist interview at Coinbase, Technical Phone Screen round, covers how they worked through the question, what the panel pushed back on, and what they would do differently.
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