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Amazon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Amazon data engineer interview with a SQL-heavy focus. Got hit with a classic Leetcode problem on consecutive date ranges and attendance thresholds.

Questions Asked (1)

Q1

Write a SQL query to find all dates where a stadium had three or more consecutive days with attendance of at least 100 people.

Algorithms & Data StructuresData Modeling
Author's notes

This is LC 601 in disguise.

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AI HintsAI Generated

Suggested Approach

Use window functions to identify consecutive sequences of dates where attendance >= 100. For each such date, compute the difference between the date and a row number to group consecutive dates, then filter groups having at least 3 days. Finally, select all dates from those groups.

Pro tip: Clarify whether the stadium can have multiple events per day; if so, aggregate attendance per date first. Also, consider using a self-join or window functions depending on SQL dialect, and mention performance implications for large datasets.

1. Filter qualifying dates

Select dates where attendance is at least 100, aggregating if multiple events per day exist.

2. Identify consecutive groups

Use ROW_NUMBER() and date arithmetic to assign a group identifier for consecutive dates.

3. Count group sizes

Group by the group identifier and count the number of dates in each group.

4. Filter groups with >=3 days

Keep only groups that have at least 3 consecutive dates.

5. Return all dates in qualifying groups

Select all dates from the qualifying groups, possibly ordered by date.

Key Points to Mention

  • Handling multiple events per day by aggregating attendance (SUM or MAX depending on interpretation).
  • Using window functions like ROW_NUMBER() to detect consecutive sequences.
  • The technique of subtracting row number from date to create a constant group key for consecutive dates.
  • Filtering groups with COUNT(*) >= 3.
  • Considering SQL dialect differences (e.g., date functions in MySQL, PostgreSQL, SQL Server).
  • Performance considerations: indexing on date and attendance, and avoiding unnecessary sorting.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.