CASE WHEN Statements

We are using CASE WHEN statements for our customers looking to create their own booleans. We use live connection so these cannot be added to the elasticube. We are looking to complete the following: 

CASE
    WHEN [Timeline Type] = "emergency department" AND [Vital Systolic Blood Pressure] < 90
    THEN 1 
    ELSE 0
END 

Additionally, customers would like to know the percentage of time the above is yes. Can this be completed in the function area or do we need to handle this in our transformation pipeline?