How to add 2 metrics from differents Data Sources ?

Data Studio is great to display data from data sources until you have to mix it up !

Fortunately, there was an update (February 2022) that ease the simple task such as added 2 metrics from different Data Sources.

It can come in handy when you want to debrief all of your marketing data, not just one by one.

Follow this tutorial and you will ba able to display the investment, revenue, impression, CTR... for all your web-marketing platform.

Blend Data Source

First things first, you need to create a blended data sources :

1. Click "Resource" -> "Manage Blends"
2. Click "Add a Blend". You are now in the configuration panel.
3. Check the first data sources, change it if needed.
4. Click "Join another table" and select the second data source.
5. Click "Configure join" and select "Cross" then save.
6. Remove all the dimensions for both data sources.
7. Add the metrics you want to sum in the metrics area of each data sources (you need only the basic metrics if you want to calculate. The global CTR, you don't want to add the CTR on both, you want to add the clicks and impressions on both and calculate the CTR later).
8. Name both table, name the new blended data source and save.

Your new blend data source is now created ! 

It contains all the basic metrics for both your account and you will now be able to use them in the same card or table.

Added Data 

You now wants to display added data : 

1. Withdraw a scorecard in your canvas
2. In the configuration panel, change the metrics and select "Create field."
3. Enter your formula, using all the field of your blended data source. For example you can now add the metrics "investment" from both tables.
4. Define the type if need and click Apply

Your scorecard with added data is now live and will automatically update each time you open this page.

If you want a calculated metrics such as ROAS, you need to create it from scratch such as 

"(Revenu Facebook + Revenue Google)/(Investment Facebook + Investment Google)"

A really good practice is to always include aggregate method in your formula. It avoids mistake and Google Data Studio can't extrapolate on how to do the calculation. The previous example should look like this : 

(SUM(Revenu Facebook) + SUM(Revenue Google))/(SUM(Investment Facebook) + SUM(Investment Google))