Choosing a value based on newest date, and newest value

Question

Good Afternoon,
I'm in search of help on a statement Im trying to perform in a Query transform in my ETL. So this is the scenario. I have a Value called SGSGVL which is "CYW" and in our descriptions table for the VALUE CYW we have 3 different Descriptions like Cadium Yellow, Cadium Yellow Paint and CDM Yellow and the date the description was added. What I would like to do is say:
Where in the description table = CYW, select the newest date and the most used value.
I've been told I can use a MAX statement but Im unsure exactly how to perform this in the query transform. Can anyone help? It would be GREATLY appreciated!
Thanks!

Answer 1

You won't be able to do what you are asking in one query transform - it is complicated due the fact that you need your "max" to be based on something other than the column you want returned (date and count, versus the description). Essentially, what you need to do is:
QUERY1: value, description, field named REC_CNT with mapping of count(*), field named MAX_DATE with mapping of max(date), group by value and description
QUERY2: reads from QUERY1 --> value, field named MAX_REC which has a mapping such as: max(lpad(REC_CNT,'0',5) || '_' || to_char(date,'YYYYMMDD')), and group by value only
QUERY3: also reads from QUERY1 --> value, description, field named THIS_REC which has mapping such as: lpad(REC_CNT,'0',5) || '_' || to_char(date,'YYYYMMDD'), no group-by
QUERY4: joins QUERY2 and QUERY3 on QUERY2.MAX_REC = QUERY3.THIS_REC. Pull the value and description from QUERY3.
Basically - QUERY2 gives you the list of records which are considered the max, and QUERY3 gives you the full list with the same column to be able to join on, so QUERY4 pulls the descriptions only for the max record.
-Trevor