Common Type 2 SCD Anti-patterns


Slowly Changing Dimension (SCD) is great for tracking historical changes to dimension attributes. SCDs have evolved over the years and besides the conventional type 1 (update), type 2 (add row) and type 3 (add column), now there are extensions up to type 7 including type 0. Almost every DW/BI project has at least few type 2 dimensions where a change to an attribute causes the current dimension record to be end dated and creates a new record with the new value. Continue Reading

PowerPivot: DAX Expression for Type 2 SCD Lookup

The greatest strength of PowerPivot is it’s ability to create relationship with different sources of data and piggyback on this relationship for various kinds of analysis. PowerPivot relationship requires one-to-many relationship between the parent and child tables. But what happens if the relationship between parent and child tables is many-to-many instead? For e.g. you might want to establish a relationship between a fact table that has a Business Key to the dimension table and that dimension table maintains history. In this post I explain how to establish a relationship between two tables that do not exhibit one-to-many relationship on their Business Key using a technique that is similar to an ETL Type 2 SCD lookup using Data Analysis Expressions (DAX). Continue Reading

Alternatives to SSIS SCD Wizard Component

SSIS comes with an out-of-box SCD Wizard to handle Type 1 and Type 2 Slowly Changing Dimensions (SCD) which is a fundamental ETL requirement. However the SCD wizard component has some serious drawbacks – both from operational and functional perspectives that make it unusable for practical purposes. A good summary on the shortcomings of SCD Wizard component can be found here

Several workarounds have evolved over time and in this post I would like explore the different alternative options to handle Type 1 and Type 2 SCD without using the out-of-box SCD Wizard Component.   Continue Reading