HASH OUTER JOIN
Short Description
A method for joining large data sets. Outer joins will return data that include unmatched rows from one or both tables.
Detailed Description​
A method for joining large data sets. The database uses the driving (parent) table table build a hash table on the join key in memory. It then probes hash table based on the values form the driven (child ) table.
Non matched and NULL child rows are returned.
The hash table will be built in memory and if insufficient memory is allowed, it will spill to disk in the TEMPORARY tablespaces impacting performance.
Further Reading​
- Oracle Magazine - How to read an execution plan
- Oracle Tuning Guide - Explaining and Displaying Execution Plans
- Oracle Tuning Guide - Comparing Execution Plans Tutorial
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