Use name of controllers to find table name in Select - sql

Question

I want to extract a ID , User_ID value from one of the Companies and Contract tables, depending on the ContorollerName value.
select P.TitleProject, P.StartDateProject, P.EndDateProject,P.ControllerID,P.RecordID,P.IsAllocated,P.ProjectStatus_ID,
CN.ControllerName,CN.PersianName,
PU.ProjectID,PU.UserID,PU.RoleID,
CASE
WHEN CN.ControllerName = 'Company' THEN
Companies.Id,Companies.[User_Id]
WHEN CN.ControllerName = 'Contract' THEN
Contracts.Id,Contracts.[User_Id]
END
from Projects P
left outer join Controllers CN ON P.ControllerID = CN.Id
left outer join ProjectUsers PU ON P.Id = PU.ProjectID
where P.IsAllocated = 1
For example, if ContorollerName is 'Company' , the select command is as follows :
select P.TitleProject, P.StartDateProject, P.EndDateProject,P.ControllerID,P.RecordID,P.IsAllocated,P.ProjectStatus_ID,
CN.ControllerName,CN.PersianName,
PU.ProjectID,PU.UserID,PU.RoleID,
Companies.Id,Companies.[User_Id]

Answer 1

You are on the right track -- using left join. But you need to add the tables to the from clause with the appropriate logic.
The logic for the join is quite unclear. The query looks something like this:
select . . .,
coalesce(c.id, co.id) as id,
coalesce(c.user_id, co.user_id) as user_id
from Projects P left join
Controllers CN
on P.ControllerID = CN.Id left join
ProjectUsers PU
on P.Id = PU.ProjectID left join
companies c
on c.? = ? and -- no idea what the right join conditions are
c.ControllerName = 'Company' left join
contracts co
on co.? = ? and -- no idea what the right join conditions are
co.ControllerName = 'Contract'
where P.IsAllocated = 1