What SQL is

Almost every application you use — your bank, a shop, a social network — stores its information in a database, and SQL is the language for talking to it. SQL (Structured Query Language) lets you ask questions of data ("which customers are in Lagos?"), and add, change, and organise it. It's one of the most useful and enduring skills in tech, used by developers, analysts, and anyone who works with data.

What a database is

A database stores data in tables — like spreadsheets, with rows and columns. A customers table might have a row per customer, with columns for name, city, and age. SQL is how you query those tables: ask for exactly the data you want, in the form you want it.

Your first query

Here's real SQL running against a real database, right in this lesson. Press Run and see the result:

That query means "select everything from the customers table." SELECT asks for data, * means "all columns," and FROM customers says which table. The result is a table of rows — the actual customer data. You just queried a database.

SQL reads almost like English

SQL was designed to be readable. Queries often read close to a plain-English request:

"Select name and city from customers." Instead of * (all columns), we asked for just name and city. The result shows only those two columns. This readability is part of why SQL has lasted decades and is worth learning.

Why SQL is worth knowing

• It's everywhere — nearly every app and website has a database behind it, queried with SQL.
• It's not just for programmers — analysts, marketers, and product people use SQL to answer questions with data.
• It's stable — SQL has been the standard for decades and isn't going anywhere; what you learn stays useful.
• It's powerful — a few lines of SQL can answer questions that would take ages by hand.

About these lessons

Every lesson runs against a small sample database with two tables — customers and orders — that you'll get to know well. You'll write real queries and see real results immediately. The database resets each time you run, so you can experiment freely, including changing data, without breaking anything.

Your turn

Your turn

1. Run SELECT * FROM customers; and look at the result table.
2. Select just the name and city columns.
3. Notice how SQL reads almost like an English request for data.

Key points

• A database stores data in tables (rows and columns); SQL is the language for querying it.
• SELECT asks for data: SELECT * FROM table gets all columns; SELECT col1, col2 gets specific ones.
• SQL reads almost like English and has been the standard for decades — a lasting, widely useful skill.
• These lessons run real queries against a sample database (customers and orders) with instant results.