SQL Introduction

Definition: SQL (Structured Query Language) is the standard language for storing, reading, and changing data in a relational database — data organised into tables of rows and columns.

Almost every website and app keeps its data in a database and uses SQL to talk to it. Learning SQL is one of the most valuable, transferable skills in tech: the same language works with MySQL, PostgreSQL, SQLite, SQL Server, and more.

What can SQL do?

• Fetch exactly the data you want with SELECT
• Add rows (INSERT), change them (UPDATE), and remove them (DELETE)
• Filter, sort, group, and summarise millions of rows in milliseconds

The sample database

Every example in this course runs against three small tables. Get to know them:

• Customers — CustomerID, CustomerName, ContactName, Country, City, Age
• Products — ProductID, ProductName, Price, Category
• Orders — OrderID, CustomerID, ProductID, Quantity, OrderDate

Example — see all customers

SELECT * FROM Customers;

Press Run to view the whole Customers table, then explore the others with SELECT * FROM Products; or SELECT * FROM Orders;.

💡 Note: changes (INSERT/UPDATE/DELETE) really work, but the sample database resets every time you press Run — so you can experiment freely and always start fresh.