Module 00 · lesson 3
The relational model: tables, rows, columns
Remember the founder's messy notepad from the first lesson? Now GadgetHub's products live in a real products table, managed by PostgreSQL. Time to look inside it for the first time and give it its first command.
The relational model
Almost all modern databases are relational: the data sits in tables (also called relations). The table from lesson 1 is now real, in a database managed by PostgreSQL.
The products table schema
Every table has a schema — which columns it has and what's in them:
| Column | What it stores |
|---|---|
id | the product's unique number |
name | the name |
category | the category |
price | price, $ |
stock | how many are in stock |
is_active | whether it's on sale right now |
created_at | when it was added |
Your first command
To see all of a table's data, we tell the DBMS:
SELECT * FROM products;
SELECT— "show, pick";*— "all columns";FROM products— "from theproductstable".
Press Run — and the whole GadgetHub catalog appears on the right: 14 products, 7 columns. Congratulations — that's your first real SQL query! There's more to come.
Summary
- The relational model = data in tables.
- A schema is a table's columns and what they store.
SELECT * FROM <table>shows all of a table's data.