INSERT/DELETE examples in a many-to-many relationship

Question

I have three tables, Users, Roles, and a junction UserRoles.

Users       UserRoles         Roles
=======     =============     =========
UserId      UserId            RoleId
Username    RoleId            Role
Firstname   Date

My tables are joined like this:

Users.UserId -> UserRoles.UserId
Roles.RoleId -> UserRoles.RoleId 

Basically, what I am looking for is an simple example that shows:

1. How to INSERT in UserRoles a UserId and a RoleId for a specific Username with a specific Role.
2. Delete a role for a specific Username

I managed to make a simple select on Roles for a specific Username like so:

SELECT 
    dbo.Roles.Role 
FROM dbo.Roles 
INNER JOIN dbo.UserRoles 
    ON dbo.Roles.RoleId = dbo.UserRoles.RoleId 
INNER JOIN dbo.Users 
    ON dbo.UserRoles.UserId = dbo.Users.UserId 
WHERE (Username = @Username)

Answer 1

To INSERT in UserRoles a UserId and a RoleId for a specific Username with a specific Role, you need to redesign your tables such that the User table has a foreign key to the Roles tables as follows:

Users       UserRoles         Roles
=======     =============     =========
UserId      UserId            RoleId
Username    RoleId            Role
Firstname   Date
RoleId

Then insert as follows:

insert into dbo.UserRoles (UserId, RoleId, [Date])
select
    u.UserId,
    r.RoleId,
    getdate() as [Date]
from dbo.Users u
inner join dbo.Roles r
   on r.RoleId = u.RoleId
   and u.Username = @Username

To delete a role for a specific Username with the above schema:

delete r
from dbo.Roles r
inner join dbo.User u
   on r.RoleId = u.Roleid
where u.Username = @Username

EDIT: Another solution suggested by @sidux

DELETE ur 
FROM dbo.UserRoles ur 
JOIN dbo.Roles r 
    ON r.RoleId = ur.RoleId 
INNER JOIN dbo.Users u 
    ON ur.UserId = u.UserId 
WHERE (Username = @Username);