? Slow Query Optimization

? Quick Overview

Slow Query Optimization focuses on identifying and improving SQL queries that take excessive time to execute. Optimizing slow queries improves database performance, reduces server load, and enhances application responsiveness.

? Key Concepts

Slow Query Log
Execution Time Threshold
EXPLAIN Query Analysis
Indexes and Query Design
Query Refactoring

? Syntax / Theory

MySQL provides a built-in slow query log that records queries exceeding a specified execution time. Once identified, these queries can be analyzed and optimized using indexing, rewriting SQL, or schema improvements.

? Code Example – Enable Slow Query Log

? View Code Example

-- Enable slow query logging globally
SET GLOBAL slow_query_log = 'ON';
-- Log queries taking more than 2 seconds
SET GLOBAL long_query_time = 2;

? Code Example – Analyze Slow Query

? View Code Example

-- Analyze query execution plan
EXPLAIN SELECT * FROM orders WHERE customer_id = 101;

? Interactive Simulation

Scenario: Searching for 1 specific record in a table of 10,000 rows.

System Ready. Choose a method below.

? Live Output / Explanation

What Happens?

Queries exceeding the threshold are written to the slow query log
EXPLAIN shows table scans, index usage, and row estimates
Missing indexes or full table scans indicate optimization needs

? Tips & Best Practices

Always use indexes on frequently filtered columns
Avoid SELECT * in production queries
Use LIMIT when fetching large datasets
Monitor slow queries regularly
Optimize joins and avoid unnecessary subqueries

? Try It Yourself

Enable slow query log on a test database
Run queries with and without indexes
Compare execution plans using EXPLAIN
Rewrite a slow query and measure improvement