Joins are fundamental to relational database design. They combine data from multiple tables based on related information.
There are several types: INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN.
An INNER JOIN returns only the rows where the join condition is met. It provides data from both tables.
A LEFT JOIN returns all rows from the left table and matching rows from the right table.
A RIGHT JOIN returns all rows from the right table and matching rows from the left table.
A FULL OUTER JOIN returns all rows from both tables.
Here's a simple SQL query to demonstrate a join: SELECT * FROM users LEFT JOIN orders ON users.id = orders.user_id;
For a deeper dive, see [link to a more comprehensive resource].