Available value selection between 2 columns

[Anonymous]

I have 4 tables 

logins, ConnectedUsers,FacilityCode, ProviderCode.   

Basically in ConnectedUsers table i have: 

Provider_Name	System_Code	Facility_Code	RegisteredUsers
AHSE	GAYA		10
CCMS	GAYA	AA02	4
AHSE	GAYA		6

logins

EventID	System_Code	Facility_Code
01	GAYA	AA02
02	GAYA

I have a measure that calculates logins based on event ID (count), however, I want the system to check if facility code in connectedusers table is blank then it should take system_code  registered users.

[amitchandak]

@Anonymous , Can you share expected output