21 Days SQL Coding Challenges

21-Days SQL Challenge using Sakila database (pre-installed in MySQL Workbench). Daily SQL practice questions adapted from LinkedIn interview prep resources (500-SQL-Questions, 50-MAANG, 300-MNC, 800-SQL). Day-by-day solutions with explanations, progressing from SELECT/WHERE basics to advanced window functions/CTEs. Perfect for data analyst interviews practice. Daily 10~15 questions

Weekly Progress

Week 1: SQL Foundations (Sakila DB)

• Day 1: Basic SELECT practice
• Day 2: Advanced_WHERE
• Day 3: WHERE + LIMIT + CASE
• Day 4: LIMIT Practice + Subquery Filters + Prep for Aggregates
• Day 5: GROUP BY + HAVING + Aggregate Mastery
• Day 6: JOIN Practice (All Types)
• Day 7: JOIN + GROUP BY + HAVING

Week 2: Analytics Practice

• Day 8: String & Date Functions Practice
• Day 9: Mixed Aggregates
• Day 10: Data Modifications + CASE + NULL Handling
• Day 11: Update/ Delete
• Day 12: Data Cleaning (NULLs, duplicates, data quality)
• Day 13: Window Functions + Advanced Data Cleaning
• Day 14: Window LAG/LEAD + Running Totals

Week 3: Production Engineering (5x Real DBs)

• Day 15: CTEs + Subqueries + Window combinations
• Day 16: Database Design + Constraints + Analytics
• Day 17: Ecommerce Database Design + Performance Queries
• Day 18: Finance Tracker (Constraints + Triggers + Analytics)
• Day 19: Mixed Review Project – Log Analyzer
• Day 20: SQL Performance Tuning Project
• Day 21: Sales Analytics Platform (Capstone Project)

🏆 Day 21 Capstone Highlights 1️⃣ Mumbai Revenue: +25% MoM [LAG screenshot] 2️⃣ Profit Leader: Electronics ₹80k [Q10 output]
3️⃣ Top Customer: Swapnil #1 Gold ₹72k [RANK] 4️⃣ Auto Stock: TRIGGER 15→13 [test] 5️⃣ Dashboard: monthly_profit VIEW [output] 6️⃣ API Ready: GetSalesReport(2026) PROC

🛠️ Tech Stack Unlocked

120+ SQL queries (Sakila + 5x custom DBs) ✅ DDL: 3NF schemas, CHECK/UNIQUE/CASCADE ✅ Analytics: Windows/CTEs → Exec dashboards ✅ Production: Triggers/Views/Stored Procs ✅ Performance: EXPLAIN → 90% index hits, prefix indexes

📁 File Structure

├── Week1/ # Sakila daily grind (Days 1-12) ├── Projects/ # Production DBs (Days 16-21) │ ├── Day16_StudentDB.sql │ ├── Day17_EcommerceDB.sql │ ├── Day18_FinanceTracker.sql │ ├── Day19_LogAnalyzer.sql │ ├── Day20_PerformanceTuning.sql │ └── Day21_Capstone_SalesAnalytics.sql ⭐ └── README.md

🚀 Run It

# MySQL Workbench
Use sakila;           # Days 1-15
Use sales_analytics_2026;  # Capstone
Call GetSalesReport(2026); # Monthly dashboard!