SQL Practice Log

This repository features my solutions for HackerRank Medium/Advanced SQL challenges. The main goal is to practice database querying and ensure data accuracy.

Technical Focus:

• Query Accuracy: Ensuring precise results using proper JOIN logic without losing data.
• Data Aggregation: Using GROUP BY and HAVING correctly to prevent data duplication.
• Code Readability: Keeping queries clean and adding brief logical notes at the top of each file.

Challenges

• The_PADS.sql - String concatenation, sorting, and aggregate functions.
• Binary_Tree_Nodes.sql - Hierarchical data classification using conditional statements and Self JOINs.
• New_Companies.sql - Multi-level JOINs and COUNT(DISTINCT) across hierarchical tables.
• Weather_Observation_Station_18.sql - Calculating Manhattan Distance using ABS() and aggregate functions.
• Weather_Observation_Station_19.sql - Calculating Euclidean Distance using POWER() and SQRT().
• Weather_Observation_Station_20.sql - Calculating the Median value using advanced ranking and window functions.
• The_Report.sql - Non-equi JOINs (BETWEEN) and conditional sorting based on grade brackets.
• Top_Competitors.sql - Multi-table JOINs and HAVING COUNT filtering to identify full scorers.
• Ollivander's_Inventory.sql - Complex window functions and subqueries to filter minimum power wands.
• Challenges.sql - Advanced HAVING logic and subqueries to filter maximum and unique counts.
• Contest_Leaderboard.sql - Combining MAX() for highest scores and SUM() for total scores across multiple submissions.
• SQL_Project_Planning.sql - Identifying consecutive dates (Gaps & Islands problem) using ROW_NUMBER().
• Placements.sql - Comparing values across related rows using Self JOINs and table aliasing.
• Symmetric_Pairs.sql - Identifying mirrored pairs using Self JOIN and UNION logic.
• Print_Prime_Numbers.sql - Advanced sequence generation and mathematical filtering using Recursive CTE (WITH RECURSIVE) and NOT EXISTS.