Depending on your DBMS, you might be able to create a view that selects only the logged-in user's row from the Employee table, and grant access to that. For example, in Oracle, you can do something like:
create view current_employee as
(select * from employee e where e.user_id = uid);
('uid' identifies the currently logged-in user).
Of course, as others have said, the more usual scenario is not to have end-users logging in directly to the database, but to have an application that's retrieving the data on their behalf, and is responsible for limiting access.