Glossary · Database

Join

A SQL operation that combines rows from two or more tables based on a related column between them.

A JOIN is a SQL clause that combines rows from two or more tables based on a related column. The main types are: INNER JOIN (returns only matching rows from both tables), LEFT JOIN (returns all rows from the left table and matching rows from the right), RIGHT JOIN (returns all rows from the right table and matching rows from the left), FULL OUTER JOIN (returns all rows from both tables), and CROSS JOIN (returns the Cartesian product). Joins are fundamental to relational databases because data is normalized across multiple tables to reduce redundancy. Understanding joins is essential for querying real-world databases where information is spread across orders, customers, products, and other related tables.

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