Database System Concepts
7th Edition
ISBN: 9780078022159
Author: Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher: McGraw-Hill Education
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Expert Solution & Answer
Chapter 15, Problem 21E
Explanation of Solution
Extending the hash-join
- The hash-join is used to compute the natural join of two relations.
- The hash-join algorithm can be extended to compute the natural left outer join by,
- Padding the tuple tr in the probe relation with nulls, if no matching tuple is found in the build relation’s hash partition.
- Include this null padded tuple in the result as well.
- The hash-join algorithm can be extended to compute the natural right outer join by,
- Keeping a Boolean flag with each tuple in the current build relation partition which resides in memory.
- Set it whenever any probe relation tuple matches the above tuple.
- Finally, Pad with null those tuples which do not have their flags set and include them in the result.
- The hash-join algorithm can be extended to compute the natural full outer join by performing natural left outer join and natural right outer join together.
Example:
Consider the customer and depositor relations given below:
customer_name | customer_address | customer_city |
Adam | Park Street | Brooklyn |
Eve | Main Road | Rye |
John | Bell Cross | Harrison |
Jane | Sand Hill | Woodside |
Tom | Walnut | Pittsfield |
Jerry | Alma | Alabama |
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