hi,
I think You use MS Access before.
It is not possible to create such drop down list using pgAdmin, but it is possible to limit acceptable values in field "student_type" in few different ways. Still this will not be a drop-down or combobox filed.
eg:
You can use table with dictionary and then use foreign key,
You can use constraint to check inserted value
You can use domain (field is in type of Your domain, and domain is based on proper constraint)
You can use trigger (before insert or update)
etc.
Regards,
