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Introduction to Tuning in SQL

SQL tuning (or SQL performance tuning) is the process of improving the performance of SQL queries to make them run faster and more efficiently. This is especially important when working with large datasets or high-traffic systems.

Why we need tuning​

  • Faster data retrieval
  • Reduced resource usage (CPU, memory, I/O)
  • Better scalability and responsiveness
  • Lower cost in cloud or production environments

Common SQL Tuning Techniques​

  • Use Indexes Wisely

    • Index frequently queried columns (especially those in WHERE, JOIN, ORDER BY, GROUP BY).
    • Use covering indexes to avoid table lookups.

  • Avoid SELECT

    • Only select the columns you need.
    • SELECT * loads unnecessary data and slows down performance.

  • Write Better WHERE Clauses

    • Use filters that leverage indexes.
    • Avoid functions or operations on indexed columns (e.g., WHERE YEAR(date) = 2024 is bad).

  • Use Joins Smartly

    • Prefer inner joins when possible.
    • Ensure joined columns are indexed.
    • Avoid joining unnecessary tables.

  • Analyze Execution Plans

    • Use EXPLAIN, EXPLAIN PLAN, or AUTOTRACE (depending on your DBMS) to understand how your query is executed.
    • Look for full table scans, nested loops, or missing indexes.

  • Avoid N+1 Queries

    • Fetch data in batches or with joins instead of making many small queries in a loop.

  • Use LIMIT / OFFSET Carefully

    • For pagination, consider using keyset pagination instead of large OFFSETs.

  • Optimize Subqueries

    • Turn correlated subqueries into joins or use CTEs (Common Table Expressions).

  • Use Caching Where Appropriate

    • Cache frequently accessed data or results of expensive queries.

  • Keep Statistics Updated

    • The query optimizer relies on statistics. Make sure they are up to date.

Tools to Help with Tuning​

  • Using EXPLAIN query, report tools to analyze what make the query slow.