Explain MySQL's EXPLAIN statement and its output.

EXPLAIN shows how MySQL executes a query and helps optimize performance.

Key columns:
• select_type: Type of SELECT
• table: Table being accessed
• type: Join type (ALL, index, range, ref, eq_ref)
• key: Index used
• rows: Estimated rows examined
• Extra: Additional information

Example:
EXPLAIN SELECT * FROM users WHERE email = 'test@example.com';
-- Shows if index is used and query efficiency