lesson 01 SQL foundations · beginner

Meet your first SELECT

Choose columns and read rows from a table.

the idea

A table is a collection of rows and named columns. SELECT chooses the columns you want to see; FROM names the table. A query reads data without changing it.

tables in this lesson

The challenges use this data. Each column shows its type underneath; → marks a link to another table.

customers4 columns · 8 rows

idinteger · key	nametext	citytext	joined_attext
1	Alice	Chicago	2024-01-10
2	Ben	Austin	2024-02-12
3	Cara	Seattle	2024-03-05
4	Dev	Chicago	2024-04-20
5	Elena	NULL	2024-05-01

showing 5 of 8 rows

products4 columns · 6 rows

idinteger · key	nametext	categorytext	pricereal
1	Notebook	Stationery	12
2	Desk lamp	Home	45
3	Keyboard	Tech	80
4	Pen set	Stationery	8
5	Headphones	Tech	120

showing 5 of 6 rows

example

The idea in one query. Press Run to see what it returns; running examples never affects your progress.

example.sql

SELECT name, city
FROM customers;

Watch for: SELECT * includes extra columns. Return only the columns the task asks for.

build it step by step

Each step changes one thing. Run them in order and watch the result change.

1
Start with a table. Every row is one customer. Read all columns first.
step-1.sql
sql›
```
SELECT *
FROM customers;
```
2
Choose two columns. SELECT changes the visible columns, not the underlying rows.
step-2.sql
sql›
```
SELECT name,city
FROM customers;
```