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Hash join

Posted on 2011-03-24
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What is a hash join?
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Question by:msimons4
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sdstuber earned 2000 total points
ID: 35206938
This is a high level description

when you hash join two rowsets  each row in each set has a hash value generated for it.
When comparing two rows to see if they match, the hash values are compared, rather than the column values themselves.

This is useful because  the hashing creates a hash table that acts like mailboxes.  To compare two rows, you simply check if they both resolve to the same "address" because they have the same hash value.  This is fast.

The downside is the hash table consumes memory and the generating of hash values takes time.



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