How do you handle changes in natural key values in BI reporting and analysis?

1 What is a natural key?

A natural key is a column or a combination of columns that can uniquely identify a record in a source system, such as a customer ID, a product code, or a date. Natural keys are often used as primary keys in relational databases, because they ensure data integrity and avoid duplication. However, natural keys can also change over time, due to business reasons or data quality issues. For example, a customer ID might change if a customer merges with another company, or a product code might change if a product is reclassified.

2 What is a surrogate key?

A surrogate key is a column or a combination of columns that can uniquely identify a record in a target system, such as a data warehouse, a data mart, or a BI tool. Surrogate keys are often generated by the ETL (extract, transform, load) process, and are not derived from any business logic or source data. Surrogate keys are usually numeric, sequential, and immutable, meaning they do not change over time. For example, a surrogate key might be a row number, a hash value, or a GUID (globally unique identifier).

3 Why use surrogate keys in BI?

Surrogate keys offer several advantages over natural keys in BI, particularly when dealing with changes in natural key values. For instance, they can preserve historical data and enable point-in-time analysis, even if a customer ID changes. Additionally, surrogate keys can simplify data modeling and join operations, even if multiple source systems have different natural keys. Furthermore, they can improve performance and scalability, as shorter and simpler surrogate keys can reduce storage space and query time, compared to large or complex natural keys.

4 How to generate surrogate keys in BI?

When it comes to generating surrogate keys in BI, there are various methods to choose from, depending on the ETL tool, the target system, and the business requirements. For instance, you can use built-in functions or operators, such as ROW_NUMBER, IDENTITY, or SEQUENCE in SQL, or AutoNumber in Access. Alternatively, you can create hash values, GUIDs, or other algorithms with custom logic or scripts, such as Python, Java, or C#. Lastly, you can use third-party tools or services, such as SSIS (SQL Server Integration Services), Informatica, or Snowflake, to generate surrogate keys automatically or manually.