Query Optimization & EXPLAIN Analysis

📄 MySQLLesson 15Advanced

Slow SQL queries impact application scalability. Using the EXPLAIN analyzer identifies bottlenecks and helps you optimize keys.

1 EXPLAIN Statement

SQL — Query Execution Plan

# Analyze query execution path
EXPLAIN SELECT * FROM users WHERE email = 'balaji@test.com';

# Key properties returned by EXPLAIN:
# - type: scan type (const/eq_ref are fast, ALL is slow full-table scan)
# - possible_keys: matching indexes MySQL can use
# - key: the index MySQL actually decided to use
# - rows: count of records MySQL needs to examine

2 Code Challenge

Challenge: Find a slow full-table scan query inside your application database, verify the scan pattern using EXPLAIN, and add an index to reduce scanned rows.