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Databases Beginner

What is JOIN?

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

JOINs are fundamental to querying relational databases. INNER JOIN returns rows with matches in both tables. LEFT JOIN returns all rows from the left table plus matches from the right. RIGHT JOIN is the reverse. FULL OUTER JOIN returns all rows from both tables.

CROSS JOIN produces the Cartesian product. Self-joins join a table with itself. Proper indexing on join columns is critical for performance.

Related Terms

Crosstab Query
A query that transforms rows into columns, creating a pivot table view of aggregated data.
Materialized View
A database object that stores the precomputed result of a query, offering faster reads at the cost of periodic refresh.
EXPLAIN Plan
A database command that shows how the query planner will execute a SQL query, revealing join methods, scan types, and estimated costs.
Normalization
The process of organizing database tables to reduce data redundancy and improve data integrity.
B-Tree Index
The default index type in most databases that organizes data in a balanced tree structure for efficient searching, sorting, and range queries.
Row-Level Security (RLS)
A database feature that restricts which rows a user can access in a table based on security policies.
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