📘 Day 95: Joins

Welcome to Day 95! Today, we'll learn about Joins, a fundamental concept in SQL for combining rows from two or more tables based on a related column between them.

Types of Joins

INNER JOIN

Returns records that have matching values in both tables.

SELECT orders.order_id, customers.customer_name
FROM orders
INNER JOIN customers ON orders.customer_id = customers.customer_id;

LEFT (OUTER) JOIN

Returns all records from the left table, and the matched records from the right table. The result is NULL from the right side, if there is no match.

SELECT customers.customer_name, orders.order_id
FROM customers
LEFT JOIN orders ON customers.customer_id = orders.customer_id;

RIGHT (OUTER) JOIN

Returns all records from the right table, and the matched records from the left table. The result is NULL from the left side, when there is no match.

SELECT orders.order_id, employees.employee_name
FROM orders
RIGHT JOIN employees ON orders.employee_id = employees.employee_id;

FULL (OUTER) JOIN

Returns all records when there is a match in either left or right table.

SELECT customers.customer_name, orders.order_id
FROM customers
FULL OUTER JOIN orders ON customers.customer_id=orders.customer_id;

Note: FULL OUTER JOIN is not supported in all SQL databases (e.g., SQLite, MySQL).

CROSS JOIN

Produces the Cartesian product of the two tables, meaning it returns all possible combinations of rows.

SELECT customers.customer_name, products.product_name
FROM customers
CROSS JOIN products;

💻 Exercises: Day 95

Please see the exercises.sql file for today's exercises.

Previous: Day 94 – Day 94: Data Query Language (DQL) • Next: Day 96 – Day 96: Subqueries

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