Tables & SELECT Queries

What is a database?

A relational database stores data in tables, like spreadsheets with strict rules. Each row is a record (one employee), and each column is a field (name, salary). Most web apps you'll work on use one: PostgreSQL, MySQL or SQLite.

Reading data

SELECT name, salary FROM employees;
SELECT * FROM employees;           -- every column (fine for exploring)

Filtering

SELECT name FROM employees WHERE salary >= 100000;
SELECT name FROM employees WHERE department_id = 1 AND hired > '2022-01-01';
SELECT name FROM employees WHERE name LIKE 'A%';  -- starts with A

Sorting and limiting

SELECT name, salary
FROM employees
ORDER BY salary DESC
LIMIT 3;

SQL keywords aren't case sensitive, but writing them in UPPERCASE is the convention and makes queries easier to scan.

The exercise runs a real SQLite database in your browser, and the test compares your result with the expected rows.