Custom Materialized View

Question

Hi
I am ha query regarding Materialized View .
Materialized View Query :
select * from emp@db1 where salary in ('1000','3000');
Scenario :
In the DB2 (Target DB) :
create materialized view emp_mv
refresh force on demand
as
select * from emp@db1 where salary in ('1000','3000');
Replication works fine .
In DB1 (Source DB) :
Update emp set salary=2000 where salary=1000 and empno=123;
Now in the DB2 (where my MV is located) , i want the existing record (salary=1000) to be still there and the new record (salary=2000) should not be present for empno=123
In DB1 (Source DB) :
Update emp set salary=3000 where salary=2000 and empno=123;
Now in the DB2 (where my MV is located) , i want the previous record (salary=1000) to be still there and the new record (salary=3000) should also be present for empno=123 (Now there should be tow records)
Is it possible ?
Any pointers is appreciated !
Thanks

Answer 1

A Materialized View is designed (intended) to give you a copy of data as the data exists in the source. If that row (with the pre-delete image) does not exist in the source, it should not exist in the MV.
How would you distinguish between the two images of the row at the MV site ? Which one is the "older" one and which is the "newer" one ? You'd have to write custom methods (tags, timestamps etc) to differentiate between the two rows.
A Materialized View is a generic solution. You cannot customize.
You have to define your own custom table (with the additional tagging methods) and your own procedures to replicate the two images of the same row. That is one of the uses of triggers. Before the row is updated, copy the preupdate image of the row (with additional column(s) for tagging the change) out to another table.
The "custom" MV can then be defined as a UNION of the two tables, the "master" table and the "audit trail" table.
You'll have to consider how you will handle DELETEs as well.
Hemant K Chitale