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ORACLE Tutorials

Indexing simplified

Indexing
What is index? Index can be defined as special kind of database object which allow you to quickly locate a particular record based on key columns. In Oracle, there a few option of index available. There are:

B-Tree Index

This type of index is suitable for:

High cardinality columns. More unique column better it will be.


Bitmap Index

Low cardinality column
Not suitable for table which DML operation occur very frequently.
Suitable for Data warehousing environment
General rule of thumb, suitable if degree of cardinality if less than 1%. Degree of cardinality means that the ratio of distinct value to the number of rows
Example:
create bitmap index person_gender_idx on cmnPerson(gender)


Bitmap Join Index
This a enhancement for bitmap index which is index is created for the join of two or more tables. This will reduce the number of data that need to be join by creating the restriction in advance. Example:

create bitmap index student_gender_idx on sisStudent(cmnPerson.gender)
from sisStudent,cmnPerson
where sisStudent.personID = cmnPerson.PersonID

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