Views: How filter Org Grps to only incl. current Group

I am using Organic Groups.

A user can be a member of multiple groups but can only work in the context of a single group at a time.

To this end, I have created a Field = Current_Group in User table (I know should not add to core tables, but found no way to get to these fields efficiently if in another table and can't do PHP).

How do I use this in a filter to limit views for that user to that single current group for that user?

In particular, how does this work for views that use aggregation?

Thanks for any suggestions.

p.s., I do not know PHP - I am a Microsoft database developer (do almost all my code that is not in SQL Server SQL) so I am trying to use only modules as much as possible.