SQL for Beginners 2025: Complete Database Query Guide

SQL (Structured Query Language) is essential for anyone working with data. Whether you're a developer, analyst, or aspiring data scientist, SQL skills are in high demand.

Basic SQL Commands

SELECT - Retrieve Data

SELECT column1, column2 FROM table_name;

SELECT * FROM customers;

WHERE - Filter Results

SELECT * FROM products WHERE price > 100;

SELECT * FROM users WHERE country = 'USA';

ORDER BY - Sort Results

SELECT * FROM products ORDER BY price DESC;

LIMIT - Restrict Results

SELECT * FROM orders LIMIT 10;

Aggregation Functions

• COUNT() - Count rows
• SUM() - Add values
• AVG() - Calculate average
• MAX() / MIN() - Find extremes

GROUP BY

Group results for aggregation:

SELECT category, COUNT(*) FROM products GROUP BY category;

HAVING

Filter grouped results:

SELECT category, AVG(price) FROM products GROUP BY category HAVING AVG(price) > 50;

JOIN Operations

INNER JOIN

Match rows from both tables:

SELECT * FROM orders INNER JOIN customers ON orders.customer_id = customers.id;

LEFT JOIN

All rows from left table, matched from right:

SELECT * FROM customers LEFT JOIN orders ON customers.id = orders.customer_id;

RIGHT JOIN

All rows from right table, matched from left.

FULL OUTER JOIN

All rows from both tables.

Data Manipulation

INSERT

INSERT INTO users (name, email) VALUES ('John', 'john@email.com');

UPDATE

UPDATE products SET price = 99 WHERE id = 5;

DELETE

DELETE FROM orders WHERE status = 'cancelled';

Free Practice Resources

• SQLZoo: Interactive SQL tutorials
• W3Schools SQL: Beginner tutorials
• LeetCode SQL: Practice problems
• Mode Analytics: SQL tutorial with real data
• HackerRank: SQL challenges

SQL is one of the most practical skills you can learn. Start with SELECT queries, practice daily, and you'll be querying like a pro! ?