In Type 2 Slowly
Changing Dimension, a new record is added to the table to represent the new
information and old records are updated. Therefore, both the original and the
new record will be present. The new record gets its own primary key.
Example: Consider
dimension table with supplier information, such as supplier name, supplier ID
and year. When the name of the supplier changes, a new row is added to the
table with latest name and the previous row is retained by adding a new column
There are three types of Type 2
Slowly Changing Dimensions
- Version Data Mapping
The
Type 2 Dimension/Version Data mapping filters source rows based on user defined
comparisons and inserts both new and changed dimensions into the target. Here
changes are tracked by versioning the primary key .Version number is created
for each dimension rows.
The
current version will have the highest version and highest value for the primary
key.
- Flag Current Mapping
In
Flag Current Mapping the changes are tracked by flagging the current
version of each dimension and versioning the primary key. For the current
version of the dimension the current flag is set to 1 and the primary key will
be the highest.
Use
the Type 2 Dimension/Flag Current mapping to update a slowly changing
dimensions table when you want to keep a full history of dimension data in the
table, with the most current data flagged. Versioned primary keys track the
order of changes to each dimension.
- Effective Date Range Mapping
Here changes are tracked by
keeping effective dates for each version of the dimension in the target. In Effective Date Range Mapping each record will
have Start date and End Date. For the current version of the record the start
date will be current date and end date will be default date (max date).
Use
the Type 2 Dimension/Effective Date Range mapping to update a slowly changing
dimensions table when you want to keep a full history of dimension data in the
table.
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