Maintain history in DW

Question

hi,
how the best way to maintain history records into a DW?
i think create start date and end date columns in tables.
i would like how create mapping?
robson

Answer 1

Hello Malathi,
There are different approaches. The one I described some time ago works with two mappings for each table you want to keep history (SCD II) although the logic could also be placed in one mapping.
In the first mapping I use an external table that contains my source data. I use a set operator to subtract all of the valid target records from the records of the external table. The SQL statement the OWB generates in principle looks like this one:
select * from source_table
minus
select * from target_table
where target_table.valid_to_date = to_date('9999-12-31','YYYY-MM-DD')
The output of the set operation contains all my new records from the source table that were not already present in the target table. Therefore I can simply insert this records into the target table. I use a sequence for the surrogate key.
In the second mapping I'm doing it just the other way round so that the SQL statement the OWB creates in principle looks like this one:
select * from target_table
where target_table.valid_to_date = to_date('9999-12-31','YYYY-MM-DD')
minus
select * from source_table
The output of the set operation now contains all the records in the target table that have to be terminated (load date -1). Therefore I'm performing an update on the target table using a target filter (target filter for update: target_table.valid_to_date = to_date('9999-12-31','YYYY-MM-DD')) to make sure I only update the current version (loading type update; match by no constraints).
That's it.
Regards,
Jörg