Hash Join

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The Hash Join is an example of a join algorithm and is used in the implementation of a relational database management system.

The basic problem of a join algorithm is to find, for each distinct value of the join attribute, the set of tuples in each relation which display that value.

Applying the Hash Join algorithm on a inner join of two relations proceeds as follows: first prepare a hash table for the bigger relation, by applying a hash function to the join attribute of each row, and then scan the smaller relation and find the relevant rows by looking on the hash table.