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SQL challenge

Query problems graded on correctness and sometimes efficiency.

Assessment format

Overview

The SQL challenge tests querying and data manipulation — joins, aggregation, window functions. It checks whether you can translate a business question into correct, efficient SQL.

How it works

Assessment format
ModelQueryAggregateVerifySchemaERDJoinsJOINGroup/windowOVER()Result
ClientServiceEdgeData

Step by step, with examples

  1. 1

    Schema

    • Understand tables and keys.
  2. 2

    Joins

    • Build the query incrementally.
  3. 3

    Group/window

    • GROUP BY and window functions.
  4. 4

    Result

    • Sanity-check row counts.
    • Example: top-N per group

About this format

Query problems graded on correctness and sometimes efficiency.

Sample task

Return the top 3 customers by total spend per region.

Solution approach

Use a window function: ROW_NUMBER() OVER (PARTITION BY region ORDER BY spend DESC), then filter rn <= 3.

Tips

  • Know window functions & joins
  • Watch for NULLs
  • Use CTEs for readability

Where this content comes from

For full transparency, this content is curated and verified from these sources:

Timed online-assessment format referencesTake-home assignment templatesOppZen-authored evaluations & solutions