Query Optimization Basics — Complete Guide
Query Optimization Basics — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of SQL Server Tutorial on Toolliyo Academy.
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SQL Server Tutorial · Lesson 20 of 100
Query Optimization Basics
SQL basics → Queries → Advanced
SQL basics · 1 — SELECT · ~6 min · SQL — SQL Queries & Clauses
What is this?
Basic tuning starts with measuring: how many reads, does a filter use an index, is SELECT * pulling unused columns? Small habits prevent slow queries.
Why should you care?
A catalog query that scans every product on each page load melts CPU as the table grows.
See it live — copy this example
Run in SQL Server Management Studio (SSMS) or Azure Data Studio.
USE DataVerse;
SET STATISTICS IO ON;
SET STATISTICS TIME ON;
SELECT ProductId, Name, PriceInr
FROM dbo.Products
WHERE Sku = 'HD-100';
SET STATISTICS IO OFF;
SET STATISTICS TIME OFF;What happened?
- STATISTICS IO prints logical reads in the Messages tab.
- You compare before/after an index.
- Selecting few columns and filtering on Sku is the baseline good pattern.
Practice next
- Run the query and open the Messages tab.
- Note logical reads for Products.
- Run SELECT * for the same filter and compare reads.
- Compare WHERE Name LIKE N'%phone%' vs WHERE Sku = 'HD-100' reads.
- Turn on Include Actual Execution Plan and note Scan vs Seek.
Remember
Measure with STATISTICS IO/TIME. Select only needed columns. Filter on selective columns you can index.
Sku lookup before Black Friday
DataVerse product-by-sku API is checked with STATISTICS IO.
Outcome: Team adds an index when reads climb with catalog size.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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