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Explain pandas and SQL basics

RbcroyalbankData Engineer · Technical Screen
EasyData EngineerTechnical ScreenData Manipulation (SQL/Python)

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This question evaluates familiarity with pandas data structures (Series vs DataFrame), SQL filtering semantics (WHERE vs HAVING), and practical SQL aggregation for detecting duplicate records, assessing competencies in data manipulation, aggregation, and basic data quality checks.

You are interviewing for a Data Engineer co-op/intern role. Answer the following short technical questions.

Python / pandas:

  1. What is the difference between a pandas Series and a pandas DataFrame? Give one practical example of when you would use each.

SQL concepts: 2. What is the difference between WHERE and HAVING in SQL, and when should each be used?

SQL query task: 3. You have a table:

customer_events

  • event_id BIGINT
  • customer_email STRING
  • source_system STRING
  • created_at TIMESTAMP

Assume created_at is stored in UTC. Write a SQL query to find duplicate customer_email values in the table. A duplicate means the same customer_email appears more than once in the full table. Return these output columns:

  • customer_email
  • duplicate_count

Only include emails that appear more than once.