Pruning itself means to cut the dead parts and work on the pieces which are indeed important one.
In Oracle partition pruning works in the same manner. Oracle can recognize which partitions and sub-partitions need to be eliminated and which partitions should be accessed for the query to be processed.
When you have created some partition on the table and you are using joins or where condition when accessing the same table , oracle prune the partition which are not needed for the output of query and scans partitions which are actually for the query and gives faster output.
For Instance , just think of the table with 12 partitions of each month of the year. And each partition contains millions of records . You are querying the same table and you want data of specific 3 months.
Traditionally oracle scans the whole table and all millions of records of the table.
With partition pruning you will find substantial improvements with oracle partition pruning.
To see partition pruning takes effect you need to check execution plan of the query.
In next post we will see how partition pruning takes place .
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