⚡ SQL Query Optimization Case Studies

Real-world SQL performance optimization examples with detailed analysis, before/after metrics, and best practices. All case studies based on production scenarios.

📊 Case Studies Overview

⭐ Case #1: Slow JOIN Query Optimization

Problem: Report taking 15+ seconds to load
Solution: Strategic indexing + query rewrite
Result: 54x faster (15.2s → 0.28s) | 98% improvement

Key Learning: Never use SELECT *, index date columns

---

⭐ Case #2: Missing Index on WHERE Clause

Problem: User search by email taking 2.8 seconds
Solution: Create unique index on email column
Result: 933x faster (2.8s → 0.003s) | 99.9% improvement

Key Learning: Index columns used in WHERE/JOIN

---

⭐ Case #3: N+1 Query Problem

Problem: 101 database queries for product listing
Solution: Use JOIN instead of loop queries
Result: 56x faster (8.5s → 0.15s) | 99% fewer queries

Key Learning: Avoid multiple queries in loops, use JOINs

---

🎯 Optimization Techniques Covered

✅ Index Strategy

• Creating strategic indexes
• Covering indexes with INCLUDE
• When to use UNIQUE indexes

✅ Query Rewriting

• Avoiding SELECT *
• Proper JOIN usage
• Query hints and optimization

✅ Performance Analysis

• Reading execution plans
• Identifying table scans
• Measuring improvements

✅ Common Problems

• N+1 query problem
• Missing indexes
• Inefficient JOINs

📈 Combined Results

Total Performance Improvements:

• Average speed increase: 348x faster
• Average improvement: 98.7%
• Total optimization impact: 3 critical queries fixed

🛠️ Tools & Environment

• DBMS: SQL Server 2019
• Tools: SSMS, Execution Plan Analyzer, SQL Profiler
• Methodology: Analyze → Optimize → Measure → Document

💡 Best Practices Summary

1. ✅ Always analyze execution plans
2. ✅ Index columns used in WHERE, JOIN, ORDER BY
3. ✅ Select only needed columns (avoid SELECT *)
4. ✅ Use JOINs instead of multiple queries
5. ✅ Test with production-like data volumes
6. ✅ Monitor and measure improvements
7. ✅ Document your optimizations

🚀 Coming Soon

• Case #4: Subquery vs JOIN performance
• Case #5: Stored procedure optimization
• Case #6: Partitioning large tables
• Case #7: Query timeout issues

👤 About

Created by: Rika Afriyani
Role: Junior Database Administrator @ PT PLN Icon+
Specialization: SQL Server performance tuning & optimization

📧 rikajo1990@gmail.com
💼 LinkedIn
🐙 GitHub

---

⭐ Found these optimizations helpful? Star this repo!

💬 Questions or suggestions? Feel free to open an issue or reach out!

---

Last updated: December 2025