1. Materialized views (snapshot tables)
Using Oracle
Materialized views

2. Ordinary views vs. materialized views
Virtual table
Named select statement
Part of the SQL standard
Syntax
CREATE VIEW viewName AS selectStatement
Physical table
Replication of master data at a single point in time
Not part of the SQL standard
Syntax
CREATE MATERIALIZED VIEW viewName AS selectStatement
Materialized views

3. Why use materialized views?
Replicate data to non-master sites
To save network traffic when data is used in transactions
Cache expensive queries
Expensive in terms of time or memory
Example: Sum, average or other calculations on large amounts of data
Materialized views

4. Refreshing a materialized view
Refresh types
Complete refresh
Recreates the materialized view
Fast refresh
Only changed data is refreshed
Initiating a refresh
Scheduled refresh
On-demand refresh
execute DBMS_REFRESH.REFRESH('hr_refg')
Materialized views

5. Different kinds of materialized views
Read-only
Insert, update or delete NOT allowed
Updateable
Insert, update and delete on the view is allowed
Changes made to the view are pushed back to the master tables at refresh
SQL syntax
CREATE MATERIALIZED VIEW viewName FOR UPDATE AS aSelectStatement
Writeable
Changes made to the view are NOT pushed back to the master tables at refresh
Same as updateable. The difference lies in the definitio of “refresh groups” …
Materialized views

6. References and further reading
Oracle9i Advanced Replication Release 2 (9.2)
3 Materialized View Concepts and Architecture
Oracle® Database SQL Reference 10g Release 2 (10.2)
CREATE MATERIALIZED VIEW
Materialized views