Databases Reference
In-Depth Information
Detect an existing business key and changed data.
If an incoming source row
contains a business key value that exists in the cross-reference table, the SCD
Type 2 Loader compares attribute values between the source row and the
cross-reference table. If the source data differs from the concatenated data, write
the source row into the dimension table as the new current row for that business
key. Add data as specified to complete the change tracking and generated key
columns. Update the cross-reference table and evaluate to the next source row.
Figure 12.3
Change Detection, Change Tracking, and Key Generation for Slowly
Changing Dimensions
The preceding diagram shows how the Begin Current and End Current columns
are updated. The new current row receives a date/time value in Begin Current,
and End Current receives a place-holder value. In the former current row, the
place-holder value in the End Current column is replaced by a date/time value.
The date/time values can be supplied in the source data, or they can be generated
by the SCD Type 2 Loader using expressions.
Detect an existing business key with no data changes.
If the business key in a
source row matches a business key in the cross-reference table, and if the attribute
values in the source row match the attribute values in the cross-reference table, do
not write the source row into the dimension table. Move to the next source row.
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