Query Optimization Basics — Complete Guide
Query Optimization Basics — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of MySQL Tutorial on Toolliyo Academy.
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MySQL Tutorial · Lesson 20 of 100
Query Optimization Basics
Basics → Advanced
Basics · 1 — SQL · ~6 min · MySQL — Queries & Clauses
What is this?
Query optimization means writing SQL and indexes so MySQL reads fewer rows and pages. Start with selective WHERE, proper indexes, and EXPLAIN to see the plan.
Why should you care?
A full scan on DataFlow orders at Flipkart scale would timeout every checkout report — indexes turn minutes into milliseconds.
See it live — copy this example
Run in MySQL Workbench or the mysql CLI.
CREATE INDEX idx_orders_customer ON orders(customer_id);
EXPLAIN SELECT order_id, total_inr
FROM orders
WHERE customer_id = 42;What happened?
- Index on customer_id lets InnoDB seek matching rows instead of scanning all orders.
- EXPLAIN shows type=ref or range and key=idx_orders_customer when optimization works.
Practice next
- Run EXPLAIN before creating the index — note type ALL.
- CREATE INDEX; run EXPLAIN again.
- Compare rows examined estimate.
- Covering index lesson preview: index (customer_id, total_inr).
- Run ANALYZE TABLE orders; after bulk insert.
Remember
Indexes support selective WHERE/JOIN. EXPLAIN previews the execution plan. Measure before and after on realistic row counts.
DataFlow customer order list
API filters orders by customer_id millions of times daily — idx_orders_customer avoids table scans.
Outcome: P99 latency drops from seconds to milliseconds.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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