Question asked by Visitor Gnaneshwar

What is materialised view?
Compare normal view and materalised (snapshot) view?
What Bitmap Index? Compare with normal index?

Hi,

Materialized view is a also type of view. It is basically used in the datawarehousing environment. For generating report sort of thing this mat. view.

If to use the normal view, we need to explictly say the view name. But the optimizer by default checks the materialized view if it is available and uses it. (Just like how it finds the index).

Now coming the index.

By default the default index is B-Tree(Balanced-Tree) index. The difference between this and bitmap is :
1.Bitmap is mainly used in the columns where it contains the low-cardinal values.
2.The efficiency and the performance of using Bitmap in low cardinal valued columns is great. Why because it uses bitmap values (biinary values 0,1) to store the information.

Hope this helps

Balasubramanian.J

hi,

The big difference between View and Materialise view , is a view will not take space in the memory where as a materialised view will take some space in the memory.

Bitmap indexes are generally used for dataware housing. The reason is these indexes are suitable only for the columns with low cordinality(low uniqueness). As the data in the dataware house is not normalised in nature, these indexes are best suitable.It will create an index for every column with o's and 1's.

General index will be based on the address, it will create an address for every row in the table.

>>What is materialised view?
- A materialised view is a database object that stores the result of a query in a database.
- A materialised view allow you to maintain copies of remote data on your local node.
- Materialized views, which store data based on remote tables are also, know as snapshots.


>>Compare normal view and materalised (snapshot) view?
-A view contain no data of its own but it is like a window through which data from tables can be viewed or changed where as materialised view stores the output of a query in database.
-After the update, the view data matches the table data but the materialized view data does not.Data in materialized views must be refreshed to keep it synchronized with its base table.

>>What Bitmap Index?
A bitmap index is a type of index that uses a string of bits to quickly locate rows in a table.


>>Compare with normal index?
Conventional wisdom holds that bitmap indexes are most appropriate for columns having low distinct values—such as GENDER, MARITAL_STATUS, and RELATION. This assumption is not completely accurate.

For clear explanation with examples follow the link