🔍 Let’s Go Deeper Into the SQL World!

Hey future data wizards! 🧙‍♂️ You've made it to Day 7 of the SQL Learning Challenge! That’s a HUGE milestone! Today we dive into a slightly deeper but super exciting concept: Subqueries.

🧠 What is a Subquery?

A subquery is just a query within another query. Think of it like a mini detective working inside your big detective! 🕵️‍♂️

They help answer more complex questions and make your queries smarter. 😎

🧪 Use Case 1: Students Who Scored Above Average

SELECT NAME, MARKS
FROM student
WHERE MARKS > (SELECT AVG(MARKS) FROM student);

🎓 Explanation:
We want to find all students who scored more than the average of the class.

👉 The part inside the parentheses (SELECT AVG(MARKS) FROM student) is the subquery.
👉 It finds the average marks, and the outer query shows students whose marks are above that average.

🔥 Cool, right? We’re comparing students with the entire class average dynamically!

🎲 Use Case 2: Students with Even Roll Numbers

SELECT NAME, ROLLNO
FROM student
WHERE ROLLNO IN (SELECT ROLLNO FROM student WHERE ROLLNO % 2 = 0);

🎓 Explanation:
We want to display students who have even roll numbers.

👉 The inner query finds all even roll numbers.
👉 The outer query then shows names and roll numbers of students who match.

🎉 Boom! Clean and powerful!

🎯 Other Cool Examples of Subqueries:

✅ 1. Students Who Have Highest Marks:

SELECT * FROM student
WHERE marks = (SELECT MAX(marks) FROM student);

✅ 2. Students with Lowest Marks in City 'Pune':

SELECT * FROM student
WHERE marks = (SELECT MIN(marks) FROM student WHERE city = 'Pune');

✅ 3. Total number of students in a particular city:

SELECT city, (SELECT COUNT(*) FROM student WHERE city = 'Mumbai') AS total_in_mumbai
FROM student;

🎮 BONUS: FUN INTERACTIVE PROJECT – “SQL BATTLE ARENA” 🎮

Let’s create a mini project that helps you revise ALL your SQL concepts learned over the last 7 days.

---

🏰 Project Name: SQL Battle Arena – Student vs Database!

👇 Project Summary:

You’re a Student Warrior 🧑‍🎓 armed with SQL queries. Your goal is to complete all stages by solving different SQL puzzles involving:

---

🏗️ Database Design:

Table: STUDENT

Table: COURSE

---

🔥 Sample Tasks by Level:

🧱 Level 1: Basic SELECT

SELECT * FROM student WHERE marks > 80;

🔗 Level 2: JOIN

SELECT s.name, c.coursename 
FROM student s 
JOIN course c 
ON s.rollno = c.stu_id;

🎲 Level 3: Aggregates

SELECT city, COUNT(*) 
FROM student 
GROUP BY city;

🔁 Level 4: GROUP BY + HAVING

SELECT city, AVG(marks) 
FROM student 
GROUP BY city 
HAVING AVG(marks) > 80;

🧩 Level 5: Subquery

SELECT name, marks 
FROM student 
WHERE marks > (SELECT AVG(marks) FROM student);

💥 Final Boss: JOIN + Subquery

SELECT s.name, c.coursename 
FROM student s 
JOIN course c 
ON s.rollno = c.stu_id 
WHERE s.marks > (SELECT AVG(marks) FROM student);

🎓 Conclusion – You Did It!

You’ve completed 7 days of focused SQL learning — from basic queries to subqueries and joins — and even built a fun review project!

✨ "SQL is not just about databases, it's about thinking logically and asking powerful questions to your data." – Your Inner Data Guru

If you ever get stuck or just need a quick refresher, I’ve got you covered.

👉 Check out my complete SQL Cheatsheet here:
🔗 Click to View on GitHub

Keep it simple. Keep learning. And keep querying! 😉🧠

Keep querying and stay curious! 🚀📊

#SQLMaster

#QueryLikeAPro

#7DaySQLChallenge