select * from custGroup;
CustGroup table exists in Aot, but giving error not declared how to make reference of this table in project?
Unfortunately you forgot to attach a tag with your version of AX (please always do it), but I assume that you're using Dynamics 365 for Finance and Operations and your code is in a package that doesn't have a reference to the package containing CustGroup (which is Application Suite). If you want to be able to use CustGroup there, open Dynamics 365 > Model Management > Update model parameters, find your model and add a reference to Application Suite.
By the way, please post developer-related questions in the developer forum.
Thank you, sure will attach tag next time.