Heavily polymorphed table - sql

Question

I have a table events. Each event can be 'initiated' and/or 'received' by a User, Visitor or a Team and I want to model these associations.
I am thinking something like
Event
type
user_actor_id
user_subject_id
visitor_actor_id
visitor_subject_id
team_actor_id
team_subject_id
Where the actor/subject refers to who initiated/received the event
Is this the correct approach? Seems like I store a lot of redundant data and I'd have to do a lot of conditional joins as it would like to query the table and get a result like
actor_id:
actor_type (either user, visitor or team)
UPDATE:
Then i'd do a select query like this
select
coalesce(ua.id, va.id, ta.id) as actor_id,
(CASE WHEN ua.id IS NOT NULL THEN 'user' WHEN va.id IS NOT NULL THEN 'visitor' ELSE 'team' END) as author_type,
(CASE WHEN ua.id IS NOT NULL THEN ua.display_name WHEN va.id IS NOT NULL THEN va.name ELSE ta.name END) as author_name,
(CASE WHEN ua.id IS NOT NULL THEN ua.avatar WHEN va.id IS NOT NULL THEN va.avatar ELSE ta.icon END) as author_name
from events e
left join users ua on ua.id = e.user_actor_id
left join users us on us.id = e.user_sibject_id
left join visitors va on va.id = e.visitor_actor_id
left join visitors vs on vs.id = e.visitor_sibject_id
left join teams ta on ta.id = e.team_actor_id
left join teams ts on ts.id = e.team_sibject_id

Answer 1

I would do the following:
create table tPeople ( -- contains as many rows as there are people
int ID,
nvarchar(max) Name
)
create table tRole ( -- contains three rows: Visitor, Team, User
int ID,
nvarchar(max) Name
)
create table tPeopleRole ( -- associates people with roles
int People_ID, -- FK to tPeople.ID
int Role_ID -- FK to tRole.ID
)
create table tEvent (
int ID,
int Type_ID,
int InitiatedPeople_ID, -- FK to tPeople.ID
int ReceivedPeople_ID -- FK to tPeople.ID
)
Then you can query tEvent and join on tPeople / tPeopleRole to get the initiator and receiver's names and/or roles.