select x.[desc],case when count(d.id) > 1 then 'True'  else 'False' end as There
from
(
	select id
	from x
	union all
	select id from y
	where person = 856
) d
join x on x.id = d.id
group by d.id,x.[desc]

drop table dbo.x,dbo.y
drop function dbo.IsThere

create function dbo.IsThere
(
	@person int,
	@id int
)
returns varchar(5)
as
begin
declare @result varchar(5)
set @result = 'False'

if exists(select 1 from dbo.y where person = @person and id = @id)
set @result = 'True'

return @result
end
go

select 
	[desc],
	dbo.IsThere(856,id) There
from dbo.x

create function dbo.IsThere
(
	@TesterID int,
	@CMCode int
)
returns varchar(5)
as
begin
declare @result varchar(5)
set @result = 'False'

if exists(select 1 from dbo.tTesterUsage inner join tTesterUsage on tLuUsage.UsageID = tTesterUsage.UsageID where tTesterUsage.TesterID = @TesterID and tLuUsage.UsageIndex = @CMCode)
set @result = 'True'

return @result
end
go

create procedure usp_tp_GetConsUsage
	@TesterID char(7)
AS
	select 
		GeneralDescription,
		dbo.IsThere(@TesterID,CMCode) as There
	from
		dbo.tUConsumer
GO

select GeneralDescription,
    case when a.UsageIndex is null then 'False' else 'True' end as There
from
 tUConsumer 
left outer join
 (select distinct tLuUsage.UsageIndex
  from
    tLuUsage
  inner join
    tTesterUsage
  on
    tLuUsage.UsageID = tLuUsage.UsageID
  where
    tTesterUsage.TesterID = @TesterID
  ) a
on
  tUConsumer.UsageIndex = a.UsageIndex