MySQL EXPLAIN Statement: Analyze Query Execution Plans

EXPLAIN shows how MySQL plans to execute a query — which indexes it will use, how many rows it expects to touch, and in what order it joins tables. It turns performance tuning from guesswork into diagnosis.

Key Points

• Prefix any query: EXPLAIN SELECT …;
• type column ranks access quality: const > ref > range > index > ALL
• 'ALL' means a full table scan — usually the red flag to fix
• key shows the chosen index; rows estimates rows examined
• 'Using filesort' and 'Using temporary' in Extra flag expensive operations
• EXPLAIN ANALYZE (MySQL 8.0.18+) runs the query and reports real timings