将维度数据汇总到单行

Question

I have a dimension with a number of attributes similar to the following which i have simplified for 1 Product and and a subset of the Columns:

What I want to be able to do is summarize: for a given ProdID, what is the current ClosedDate? when did the Current closed date begin? What is the previous ClosedDate? When did the previous ClosedDate begin?

eg from this example my answer would be:

The closed dates dont follow any particular ordering. A product doesnt have to have a Closed Date, if so it is -1.

I got as far as thinking i could use ROW_NUMBER() to index each history item as this would help with the most recent stuff, and the previous ClosedDate. I am stumped on how to get the previous Closed Date valid from, particularly in the case where I have 2 rows of history relating to 20200408.

Any suggestions appreciated.

Answer 1

One option uses solely windows functions. Assuming that ties on closedDate are broken by picking the highest historyRow , that would be:

select 
    prodID,
    closedDate as closedDateCurrent,
    validFrom as closedDateCurrentStart,
    previousClosedDate,
    previousClosedDateStart
from (
    select
        t.*,
        row_number()    
            over(partition by prodID order by closedDate desc, historyRow desc) 
            as rn,
        lag(closedDate) 
            over(partition by prodID order by closedDate desc, historyRow desc) 
            as previousClosedDate,
        lag(validFrom) 
            over(partition by prodID order by closedDate desc, historyRow desc) 
            as previousClosedDateStart
    from mytable t
) t
where rn = 1