SQL Interview Preparation

Collection of SQL solutions from various platforms with daily progress tracking.

📆 Daily Progress

April 2025

Date	Platform	Topic	Difficulty	Category	Key Concepts	Review
7	PrepVector	Duplicate Transaction	Medium	Window Functions	LAG, INTERVAL	📝
7	PrepVector	Monthly Revenue Growth	Medium	Data Analysis	LAG, COALESCE, Revenue Calculation	📝
6	PrepVector	Click Through Rate by Age	Medium	Data Analysis	COALESCE, NULLIF, Age Groups	📝
6	PrepVector	Consecutive Day Streak	Medium	Window Functions	LAG, Running Sum, CTE	📝
3	PrepVector	Third Unique Song	Medium	Window Functions	DENSE_RANK, CTE	📝
2	InterviewMaster	User Engagement	Easy	Data Analysis	DATE, DISTINCT	📝
2	PrepVector	Likers' Likers	Medium	Self Joins	JOIN, COUNT DISTINCT	📝
1	PrepVector	Product Sales by Month	Medium	Pivoting	CASE, SUM, GROUP BY	📝

March 2025

Date	Platform	Topic	Difficulty	Category	Key Concepts	Explanation
31	PrepVector	Sequential Project Pairs	Medium	Self Joins	SELF JOIN	📝
30	PrepVector	Upsold Customer Count	Medium	Aggregation	DISTINCT, DATE, CTE	📝
29	PrepVector	Above Avg Products	Medium	Aggregation	AVG, CTE, CROSS JOIN	📝
28	PrepVector	Post Completion Rate	Medium	Aggregation	SUM, CASE, CTEs	📝
27	PrepVector	Most Recent Transaction	Medium	Window Functions	ROW_NUMBER, DATE, CTE	📝
26	PrepVector	Single vs Repeat Job Posters	Medium	Aggregation	CTEs, CASE, GROUP BY	📝
25	PrepVector	Home Address Order %	Medium	Aggregation	FILTER, COUNT, JOIN	📝
24	PrepVector	Inactive User %	Easy	Joins	NOT IN, Subquery, COUNT	📝
23	Ankit Bansal	Cancellation Rate	Hard	Window Functions	PARTITION BY, AVG	📝
23	Ankit Bansal	Friends Scores	Medium	Self Joins	INNER JOIN, GROUP BY	📝
23	Ankit Bansal	Top Products (80% Sales)	Hard	CTEs	ROW_NUMBER, SUM OVER	📝
21	Ankit Bansal	Nth Sunday	Medium	Date Functions	DATEADD, DATEDIFF	📝
20	Ankit Bansal	Customer Resources Used	Easy	Group By	GROUP BY, SUM	📝
19	Ankit Bansal	New vs Repeat Customers	Medium	Window Functions	LAG, LEAD, PARTITION	📝
19	Ankit Bansal	ICC World Cup Points	Medium	Case When	CASE, SUM, GROUP BY	📝
19	Rishabh Mishra	Music Data Analysis	Easy	Basic Joins	INNER JOIN, COUNT

📚 Learning Resources

1. PrepVector Challenges

   • Practice platform for SQL interviews

2. SQL Interview Questions

   • Comprehensive video series by Ankit Bansal

3. SQL Tutorial (Hindi)

   • Beginner-friendly SQL fundamentals

📊 Statistics

• Total Problems Solved: 24
• Platforms Covered: 4
• Topics Covered: Data Analysis, Aggregations, Window Functions, CTEs, Date Functions, Conditional Logic, Self Join, Pivoting, DENSE_RANK, Running Sum, COALESCE

🛠️ Tools Used

• PostgreSQL
• MySQL Workbench
• VS Code with SQL extensions

📝 Notes

• Solutions include detailed explanations
• Each solution is tested with sample data
• Focus on performance optimization