💻 LeetCode SQL 50 - Study Plan Solutions

My comprehensive solutions to the SQL 50 study plan on LeetCode. This repository features optimized queries written in MySQL, organized by topic according to the LeetCode curriculum.

📁 Project Structure

The solutions are categorized into folders based on the specific SQL concepts they address:

Category	Focus Areas
Select	Basic data retrieval and filtering (WHERE).
Basic Joins	Relational mapping using INNER, LEFT, and RIGHT JOIN.
Basic Aggregate Functions	Data summarization (COUNT, SUM, AVG, ROUND).
Sorting and Grouping	Result organization (GROUP BY, HAVING) and ordering.
Advanced Select and Joins	Complex joins, self-joins, and conditional logic (CASE WHEN).
Subqueries	Nested queries and Common Table Expressions (CTE).
Advanced String Functions / Regex	String manipulation and pattern matching.

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💡 Key Technical Insights

Throughout this challenge, I have mastered the following advanced SQL techniques:

• Window Functions: Implementing RANK(), DENSE_RANK(), LEAD(), and LAG() for complex analytical tasks.
• CTEs (Common Table Expressions): Writing clean, modular, and maintainable code using the WITH clause.
• Complex Filtering: Identifying duplicates or unique records using window-based counting (e.g., the Insurance problem).
• Running Totals: Calculating cumulative sums and weights (e.g., the Last Person to Fit in the Bus problem).
• Performance Optimization: Using set-based logic and efficient aggregation over procedural approaches.

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🏆 Featured Solutions

#	Problem	Key Concept	Link
550	Game Play Analysis IV	Retention Logic (RANK & LEAD)	View Script
1661	Average Time of Process per Machine	Time Diff with Lead Window Function	View Script
1321	Restaurant Growth	Moving Averages (ROWS BETWEEN)	View Script
1907	Count Salary Categories	Custom Categorization with UNION	View Script
585	Investments in 2016	Multi-level Filtering (COUNT OVER)	View Script
1204	Last Person to Fit in the Bus	Running Totals (Cumulative Sum)	View Script

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🛠️ How to Use

All solutions have been verified on LeetCode and pass 100% of the test cases. To run these scripts locally:

1. Ensure you have a MySQL environment set up (e.g., MySQL Workbench, DBeaver).
2. Clone the repository:

   git clone [https://github.com/Kuba27x/SQL50-Solutions.git](https://github.com/Kuba27x/SQL50-Solutions.git)