but what I want is that a separate permission should be granted to this user in sql.
Is it possible?so when they login they access different objects.
Yes. Drop the SQL Server Login you created based on Windows Group myserver\wingrp1 and add individual SQL Server Logins for each Windows User, e.g. myserver\winusr1, myserver\winusr2 and myserver\winusr3. With this approach each SQL Server Login can have a separate set of permissions in the database instance.
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--Plato