Connect multiple SQLite database files using ATTACH

ATTACH allows you to attache another database file to the current connection.

Example:

ATTACH 'external.db' AS ext;

This makes it possible to join tables from different databases.

Example:

$ sqlite3 main.db
ATTACH sales.db AS sales;
SELECT
    e.employee_name,
    s.sale_amount
FROM
    employees AS e
JOIN
    sales.sales AS s ON e.employee_id = s.employee_id
WHERE
    s.sale_date > '2025-01-01';