SQL & Databases Masterclass Course
Welcome to the ultimate postgresql tutorial for beginners 2026. Work through interactive sql practice problems with solutions, master our comprehensive sql window functions tutorial modules, and prepare for tough sql interview questions at Google and Amazon entirely in your browser. Claim your course completion XP and build production-ready database mastery today!
SQL Lesson 1: SELECT queries 101
Introduction & Core Concept
The most fundamental instruction in SQL is retrieving data using the SELECT statement. If a database is a giant library, SELECT is how you tell the librarian exactly which books or pages you want to read.
SELECT column1, column2
FROM table_name;If you want to pull *every single column* from a table without typing them all out, you use the asterisk wildcard (*):
SELECT * FROM table_name;Why & Where We Use It
Real-World Example
Suppose marketing wants a simple list of all product names and their prices to design a promotional flyer. They don't care about inventory stock counts, supplier IDs, or warehouse shelf locations. They run a targeted SELECT query fetching strictly the name and price columns.
Best Practices: What to Do & What NOT to Do
AS new_name) to rename confusing database headers into friendly, presentation-ready titles (e.g., SELECT price AS retail_price_usd).SELECT * in production application code. If a backend engineer later adds 50 giant text columns to the table, SELECT * will suddenly start downloading massive amounts of unneeded data, slowing down your app!