ADQL for doing UNION query

[CommunityUser]

I need to compute the number of distinct users across both mobile and web application. 

For web alone I get the number using this query -

SELECT distinctcount(userdata.userId) FROM browser_records

And for mobile using this - 

SELECT distinctcount(userdata.userId) FROM mobile_session_records

What I am looking for is a way to compute the distinctcount across these two combined because some users get counted twice if I simply add the output of these two queries. How can I do this in ADQL? In SQL this can be solved using a UNION.

Thanks

[Umervali_Niyama]

Appdynamics does not have union where as ther competitors like Newrelic does provide...I was loking the same but no luck