You need to UNION your data
You can't show like "ALL" in Data Blend. Blend works like a Inner Join but not Full Join.
Note: You can show all values but, You can't merge both database.
If you want to combine and show both values then you have 2 options,
1. If your database is same then you can apply Union(Coulmn Name should be same from both DB)
2. Do Left Join
The data sources have different fields. They are two fact tables that share some dimensions. I can't union them.