Cost Efficiency Variance

A hard SQL interview practice problem on DataDriven. Write and execute real sql code with instant grading.

Domain

SQL

Difficulty

hard

Seniority

senior

Problem

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.

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