MySQL Practice Series 🔥🚀❤️‍🔥

Welcome to the MySQL Practice Repo! 🚀
This repository is perfect for practicing SQL queries including CRUD operations, Joins, Functions, Constraints, and Interview Questions preparation.

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✅ What's Inside?

• 🔹 100 Most Asked SQL/MySQL Interview Questions
• 🔹 Real-world Use Cases & Scenario-Based Queries
• 🔹 Performance Tips & Optimization Techniques
• 🔹 Window Functions, Joins, Indexing, JSON & More

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📂 How to Use

• Clone the repo
• Read through the markdown or PDF format
• Practice each question with a database like MySQL Workbench, phpMyAdmin, or DB Fiddle
• Revise before your interview or assessment

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✅ Types of SQL Commands:

👉 DDL (Data Definition Language): create, alter, rename, truncate & drop

👉 DQL (Data Query Language): select

👉 DML (Data Manipulation Language): insert, update & delete

👉 DCL (Data Control Language): grant & revoke permission to users

👉 TCL (Transaction Control Language): start transaction, commit, rollback

Keys🗝️

✔️ Primary Key: It is a column (or set of columns) in a table that uniquely identifies each row. (a unique id) There is only 1 PK & it should be NOT null.

✔️ Foreign Key: A foreign key is a column (or set of columns) in a table that refers to the primary key in another table. FKs can have duplicate & null values.

📌 Table of Contents

• 🔧 CRUD Operations
• 📋 Advanced Queries
• 🔗 Joins
• 🧠 Functions & Clauses
• 📎 Constraints
• 💬 Top Interview Questions
• 📂 Sample Database

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🔧 CRUD Operations

🟢 Create (INSERT)

INSERT INTO employees (id, name, age, department)
VALUES (1, 'Alice', 28, 'IT');

🔍 Read (SELECT)

SELECT * FROM employees;
SELECT name, department FROM employees WHERE age > 25;

📝 Update

UPDATE employees
SET department = 'HR'
WHERE id = 1;

❌ Delete

DELETE FROM employees
WHERE id = 1;

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📋 Advanced Queries

• 🔢 Aggregate Functions

SELECT COUNT(*) FROM employees;
SELECT AVG(age) FROM employees;

• 🧩 GROUP BY

SELECT department, COUNT(*) FROM employees GROUP BY department;

• 🚫 HAVING

SELECT department, COUNT(*) FROM employees
GROUP BY department
HAVING COUNT(*) > 2;

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🔗 Joins

👥 INNER JOIN

SELECT e.name, d.name AS dept_name
FROM employees e
INNER JOIN departments d ON e.department_id = d.id;

🚀 LEFT JOIN

SELECT e.name, d.name
FROM employees e
LEFT JOIN departments d ON e.department_id = d.id;

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🧠 Functions & Clauses

• ⏱️ NOW() – Current timestamp
• 🗓️ DATE() – Extract date
• 🔠 UPPER(), LOWER() – Case conversion
• 🔎 LIKE, IN, BETWEEN – Conditional filters

SELECT * FROM orders
WHERE order_date BETWEEN '2024-01-01' AND '2024-12-31';

SELECT * FROM employees
WHERE name LIKE 'A%';

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📎 Constraints

• 🔑 Primary Key
• 🗝️ Foreign Key
• 🔒 NOT NULL
• 🛡️ UNIQUE
• ✅ CHECK

CREATE TABLE students (
    id INT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    age INT CHECK (age >= 18)
);

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📂 Sample Database

You can practice with:

• employees 👨‍💼
• departments 🏢
• orders 🧾
• products 🛒
• students 🎓

Use dummy data or import from Mockaroo for realistic datasets.

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📣 Contribution

Feel free to fork this repo, add new queries, or create issue threads if you find bugs or want improvements!

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🌟 Don't forget to

• ⭐ Star the repository
• 🍴 Fork it
• 📢 Share with friends & developers preparing for interviews
• 🔁 Keep practicing daily!

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📩 Lets Connect

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"Practice makes perfect — keep querying until it's second nature!" 💪