What is the difference between Table Calculations and Calculated Fields? This is a common question for most Tableau users when they first start their Tableau journey. I must admit that I was no different when I first started. Now I can make the distinction thanks to Carl Allchin who dived into the topic in the DS6 Desktop III Training. For anyone who is not sure what the difference between Table Calculations and Calculated Fields please read ahead.
Table Calculations and Calculated Fields are similar in the sense that they both use functions to compute the results. The difference is how and where the computing takes place, where the result is saved and if it can be reused in more worksheets.
Here is a little visual representation redrawn from Carl’s class that shows where Table Calculations and Calculated Fields are computed.
Table Calculations (including the Quick Table Calculations) live in our Tableau View. They are created in the view and stay there, locally in our worksheet.
Calculated Fields are created on a data level and appear as a separate column in the data source. Tableau doesn’t change the source, but can create an extract where the calculations will be visible.
Tableau uses VIZQL and uses a data interpreter when connecting to a data source operating with SQL. Tableau reads the data and puts it up in our view. Now if we are creating a Table Calculation Tableau uses the already processed data and computes everything locally, showing the result in the view. The Table Calculation stays locally where it’s created and is not send back to the data source to be re-used.
To re-use a Table Calculation, we need to save it by dragging it in the Data Pane. This way it is saved as a Calculated Field.
Calculated Fields are created by computing with the data source and can be found in it as a new column. They stay in our Data Pane and can be re-used in different analysis easily.
The difference between the two types of calculations goes beyond where they are found. Table Calculations are simpler and their scope is more limited compared to Calculated Fields. Calculated fields are much more diverse enabling deeper analysis.