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Interview quiz track

First 2 free Intermediate SQL

SQL – Performance and Indexing

Practice SQL performance and indexing interview questions. Cover indexes, query optimization, EXPLAIN plans, and common slow-query patterns. Answer questions and receive feedback on correctness and approach. Ideal for intermediate SQL and data engineer interview prep. First 2 questions are free with full feedback.

  • Level Intermediate
  • Questions 12
  • SQL
  • performance
  • indexing
  • intermediate
  • interview practice

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Sample sql – performance and indexing interview questions

Preview 6 questions from this track in quiz order. In the full quiz you answer one at a time — type or speak — then get a score and feedback.

  1. What is a database index and why is it used?

    What a strong answer includes

    Speeds up reads; costs extra storage and slower writes.

  2. When would you add an index?

    What a strong answer includes

    Columns frequently used in WHERE, JOIN, or ORDER BY.

  3. What is the downside of too many indexes?

    What a strong answer includes

    Slower inserts/updates and more storage.

  4. Explain a covering index.

    What a strong answer includes

    Index contains all columns needed by the query.

  5. How do you identify a slow query?

    What a strong answer includes

    Uses EXPLAIN or query logs.

  6. What does a sequential scan mean in an EXPLAIN plan?

    What a strong answer includes

    Full table scan; often a sign a better index is needed.