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Advanced SQLAdvanced10 min
Indexing for Query Speed
Learn how indexes impact query plans and when to add or avoid them.
What You Will Learn
- Use composite indexes that match your most common WHERE and ORDER BY patterns.
- Avoid indexing low-selectivity columns like boolean flags on large tables.
- Validate improvements with EXPLAIN before and after changes.
Sample SQL
EXPLAIN SELECT order_id, total_amount
FROM orders
WHERE customer_id = 42
AND status = 'paid'
ORDER BY created_at DESC;Next Step
Try rewriting this query in your own schema, then use our tools to format and refine it.