You can easily check list of companies accessible to a GP user using Company Access Window. Or you can use a small query on table sy60100
FROM sy01500 WHERE cmpanyid
IN (SELECT cmpanyid FROM sy60100
WHERE userid = ‘LESSONUSER1′)
However, recently I needed a list of companies a SQL user (not user in GP) had access to. For this I needed list of databases the user had access to and company...