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Data Modelling: Star and Snowflake Schema

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Data Modelling: Star and Snowflake Schema

Topics covered in this session,




  1. What is star schema? → https://docs.microsoft.com/en-us/power-bi/guidance/star-schema

  2. What is the snowflake schema? → https://docs.microsoft.com/en-us/power-bi/guidance/star-schema#snowflake-dimensions

  3. Query Folding →https://docs.microsoft.com/en-us/power-query/power-query-folding

  4. Connect fact and dimension tables. This is also called data modelling

  5. What is one to one and one to many relationship?

  6. Why many to many relationship should be avoided? https://docs.microsoft.com/en-us/power-bi/guidance/relationships-many-to-many#:~:text=Generally%2C we don't recommend, the Order table OrderID column.

Frequently Asked Questions

Q1. I already have some relationships between the tables. Should I delete them first?

Yes, this is already covered in the first lecture of the 4th chapter, 'Install Power BI and Load Data from MySQL Database.’

Video Link: codebasics.io/courses/power-bi-data-analysis-with-end-to-end-project/lecture/876

Please check the video again from 03:00.
 

Q2. The remaining Forecast table is NOT present in the relationship model. Why?

We disabled loading the data from 'Remaining Forecast' to the data view and hence it won't be present in the relationship model. (Refer - Chapter 5 -> Power Query Best Practices -> 03:15)
The load is disabled because data from 'Remaining Forecast' is already added to the 'fact_actuals_estimate table', and it is not required to load this data separately.
(Refer Chapter 5 -> Transform Data in Power Query Editor - > ~ 03:00).
 

Q3. What's the difference between a snowflake and a star schema?

Because both are used in building relationships? Is it always recommended to build all the possible relationships between the facts and the dimension table or, we can also leave some relationships?

1. Please find this resource to get a clear idea about the star schema and snowflake schema: www.geeksforgeeks.org/difference-between-star-schema-and-snowflake-schema/

2. It is always recommended and best practice to spend a good time in building all the possible relationships in the Data model, as it helps to do more operations like joins, calculated formulas, etc.