help with function security

I wish to control access to some tables, so I do not want to grant
select to all users. Instead I would like to use some functions which
return the info.

So I have some tables owned by admin
I have a user who does not have select permission on the tables owned by
admin.
admin has created some functions which perform some selects on admin's
tables.
When user runs these functions, user gets permission denied.

Is there a way to let the user be admin when running the functions ????

You can do this with Oracle.

Any help appreciated

Regards,

Steve