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Cost Efficiency Variance

A hard SQL mock interview question on DataDriven. Practice with AI-powered feedback, real code execution, and a hire/no-hire decision.

Domain
SQL
Difficulty
hard
Seniority
senior

Interview Prompt

For each billing entry, compute the cost-per-service ratio (amount divided by the number of services in that region). Then find the monthly average of these ratios. For each year-month, show the average ratio, the monthly average, and the average absolute difference between individual ratios and that month's average.

How This Interview Works

  1. Read the vague prompt (just like a real interview)
  2. Ask clarifying questions to the AI interviewer
  3. Write your sql solution with real code execution
  4. Get instant feedback and a hire/no-hire decision