Slowly Changing Dimensions Archives

Rapidly Changing Dimension (RCD) in Data Warehouse

A dimension is a fast changing or rapidly changing dimension if one or more of its attributes in the table changes very fast and in many rows. Handling rapidly changing dimension in data warehouse is very difficult because of many performance implications. As you know slowly changing dimension type 2 is used to preserve the history for the changes. But the problem with type 2 is, with each and every change in the dimension attribute, it adds new row to the table. If in case there are dimensions that are…

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September 16, 2016

Data Warehouse

Slowly Changing Dimensions (SCD) in Data Warehouse

Slowly changing dimensions or SCD are dimensions that changes slowly over time, rather than regular bases. In data warehouse environment, there may be a requirement to keep track of the change in dimension values and are used to report historical data at any given point of time. We can implement slowly changing dimensions (SCD) using various approaches, such as; Type 0: Always retains originalType 1 : Keeps latest data, old data is overwrittenType 2 : Keeps the history of old data by adding new rowType 3 : Adds new attribute to store changed valueType 4 : Uses…

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July 3, 2016

Data Warehouse

Design Slowly Changing Dimension Type 2 in SQL Cont

This is a continuation of the Design Slowly Changing Dimension (SCD) Type2 in SQL Step 4: Copy only updated records from LOAD table These are records which are updated in this load cycle. Since updated records are already in the LOAD table, you have to compare the LOAD and TGT records on Patient ID or SK column and copy the record which is updated. You should also keep in mind to set EFF_FROM_DT and flag to indicate active record. The updated records will be active from the moment we load them so EFF_FR_DT…

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July 3, 2016

Data Warehouse

Design Slowly Changing Dimension Type 2 in SQL

Dimensions in data warehousing contain relatively static data about entities such as customers, stores, locations etc. Slowly changing dimensions commonly known as SCD, usually captures the data that changes slowly but unpredictably, rather than regular bases. Slowly changing dimension type 2 is most popular method used in dimensional modelling to preserve historical data. For example, lets take the example of patient details. The fact table may contains the information about patient expense details. The fact and dimensions are always linked by means of foreign keys. One of the dimension may contain the information about patient (say, patient dimension…

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July 3, 2016