Hash Join
Hash Join is a database query execution algorithm used to combine rows from two tables based on a join condition, typically an equality match. It works by building a hash table from one table (the build input) and then probing this hash table with rows from the other table (the probe input) to find matching rows efficiently. This algorithm is commonly employed in relational database management systems (RDBMS) for performing joins in SQL queries, especially when dealing with large datasets.
Developers should learn Hash Join when working with database performance optimization, query tuning, or database internals, as it is a fundamental algorithm for efficient data retrieval in SQL joins. It is particularly useful in scenarios involving large tables where nested loop joins would be too slow, such as in data warehousing, analytics, or applications requiring complex joins on non-indexed columns. Understanding Hash Join helps in writing better queries, interpreting execution plans, and designing databases for optimal performance.