Multiple rows with single date

Question

I am using a CDC control task to extract and load data from our OLTP source to our Data Warehouse.
For our Date dimension, we have a DateKey which is a
DATETIME stamp (created using SSAS dimension wizard). Time is always 00:00:00 as a DATETIME
value is required for populating the dates.
Our fact table destination uses this DateKey as a FK.
Our fact table OLTP data source contains multiple records with a single DATE and TIME field. This fine as I can convert the DATE field to a DATETIME using a derived column.
However, as our Date dimension has granularity of a day, all we require for our fact table is the most recent daily record from our OLTP data source.
At present, the data flow task is attempting to write all records and failing on PK constraint.
How would I go about traversing all records for each date and loading only the most recent for that day? Is there a better way to go about this?

Answer 1

If you wish to get only one record for today, you can simply use in your source query:
SELECT TOP 1 ... FROM OLTPdata ORDER BY DEATETIMEcolumn DESC
if you need one record for each date, you may use ranking functions:
WITH Q AS (
SELECT
ROW_NUMBER() OVER (PARTITION BY CAST(DateTimeColumn AS DATE) ORDER BY DateTimeColumn DESC, some tie breaker column) AS ROWNUM,
FROM  OLTPData
SELECT * FROM Q WHERE ROWNUM=1