How find out parent user roles ?

Question

user_role:

1) user_role_id

2) user_code

3) role_name

4) parent_role_id

Users

1)UserId

2)FirstName

3)LastName

4)UserRole

When we select admin role, so query should returns admin users,

When we select supervisor role, so query should returns admin users and supervisor users,

when we select staff role, so query should return supervisor users.

Following is my stored procedure, it's working fine but i want another solution.I am new in sql server.

CREATE PROCEDURE [get_parent_users]

@UserRole INT

AS

BEGIN

DECLARE @roleCode AS VARCHAR (50);

SELECT @roleCode = role_code

FROM user_role

WHERE user_role_id = @UserRole;

IF @roleCode = 'sysadmin'

BEGIN

SELECT u.UserId,

u.FirstName,

u.LastName,

u.UserRole,

ur.role_name

FROM Users AS u

INNER JOIN

user_role AS ur

ON ur.user_role_id = u.UserRole

WHERE ur.parent_role_id = 1

AND ur.user_role_id = @UserRole;

END

IF @roleCode = 'supervisor'

BEGIN

SELECT u.UserId,

u.FirstName,

u.LastName,

u.UserRole,

ur.role_name

FROM Users AS u

INNER JOIN

user_role AS ur

ON ur.user_role_id = u.UserRole

WHERE u.UserRole = (SELECT parent_role_id

FROM user_role

WHERE user_role_id = @UserRole);

END

IF @roleCode = 'staff'

BEGIN

SELECT u.UserId,

u.FirstName,

u.LastName,

u.UserRole,

ur.role_name

FROM Users AS u

INNER JOIN

user_role AS ur

ON ur.user_role_id = u.UserRole

WHERE u.UserRole = (SELECT parent_role_id

FROM user_role

WHERE user_role_id = @UserRole);

END

END

Thanks in advance