Day 88 of Learning MERN Stack

Hello Dev Community! 👋

It is officially Day 88 of my 100-day full-stack and database engineering streak! 🎯 Over the last few weeks, I built structural foundations, views, mutations, and complex multi-table joins. Today, I transitioned into a major new phase: Applying my knowledge to solve live algorithmic challenges on HackerRank! 🖥️🔥

Instead of just writing sandbox code, competitive problem-solving tests your ability to translate strict business requirements into clean, high-performance database queries under optimized time complexities.

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🧩 The HackerRank Challenges Handled Today

As showcased across my workspace scripts inside "Screenshot (191).png" and "Screenshot (192).png", I didn't just type answers on the web; I replicated the exact tables locally to verify query behaviors under the hood!

1. Challenge: Revising the Select Query I

• The Problem: Query all columns for all American cities in the CITY table with populations larger than 100,000. The country code for America is USA.
• The Execution: Layered multi-variable filtering logic using structural logic intersections (AND) to target row matrices with surgical precision:

sql
SELECT ID, NAME, COUNTRYCODE, DISTRICT, POPULATION 
FROM CITY 
WHERE POPULATION > 100000 AND COUNTRYCODE = "USA";