Creating an SCD Type 2 in T SQL without using MERGE

Question

I am attempting to create an SCD type 2 using T-SQL without MERGE (I'm not allowed to use it as a condition of the development work I am doing). I can use a CTE, but I have not tried that yet.
I have a temp table that contains ten records that I am testing with. The following is one variant of the code I have used to try and make this work:
declare 
@System_User nchar(50)
,@CurrentDate datetime 
,@MaxCheckDate datetime
set @System_User = system_user
set @CurrentDate = getdate()
--INSERT
insert dim.slot
Source_Slot_ID
,Slot_Start_DateTime  
,Patients_PerSlot
,IsSlotSearchable
,IsSlotVisible
,[Created_Date]
,[Created_By]
select
src.IdSlot
,src.SlotDateTime
,src.PatientsPerSlot
,src.IsSlotSearchable
,src.IsSlotVisible
,@CurrentDate
,@System_User
from #TmepSlot src
left join dim.Slot dest
on src.IdSlot = dest.Source_Slot_ID
left join (select source_slot_id, max(created_date) as created_date from dim.slot group by Source_Slot_ID) MaxRecord
on dest.Source_Slot_ID = MaxRecord.Source_Slot_ID
and dest.Created_Date = MaxRecord.created_date
where dest.Source_Slot_ID is null
or
src.PatientsPerSlot
<> dest.Patients_PerSlot
or
src.IsSlotSearchable <> dest.IsSlotSearchable
or
src.IsSlotVisible
<> dest.IsSlotVisible
The problem with this variation is that when I change a value in the source like src.Patients_PerSlot, and then run the query, I get the new record i expect, but when I run the query again, a duplicate record gets created. 
How do I correctly isolate the correct latest record and add the changed record without inserting that changed record more than once?
Thank you for your help.
cdun2

Answer 1

Hi,
shouldn't you use an inner join between dest and maxrecord like so:
from #TmepSlot src
left join (dim.Slot dest
inner join (select source_slot_id, max(created_date) as created_date from dim.slot group by Source_Slot_ID) MaxRecord
on dest.Source_Slot_ID = MaxRecord.Source_Slot_ID
and dest.Created_Date = MaxRecord.created_date)
on src.IdSlot = dest.Source_Slot_ID
where dest.Source_Slot_ID is null
regards,
Rudolf
Rudolf Swiers
Thanks! I don't remember when I've done a join that way, but it makes sense.
cdun2