How to efficiently version records in an SQL database

Question

In at least one application, I have the need to keep old versions of records in a relational database. When something should be updated, instead a new copy would be added and th

Answer 1

I have worked with tracking versions of records but never with overlapping ranges. However, I have experience selecting records under similar criteria. Here's a query that should do what you want.

select  *
from    t1
where   VersionId = (select top 1 VersionId
                     from   t1 as MostRecentlyValid
                     where  MostRecentlyValid.ValidFrom <= @AsOfDate
                            and (MostRecentlyValid.ValidTo >= @AsOfDate
                                 or MostRecentlyValid.ValidTo is null)
                            and t1.Id = MostRecentlyValid.Id
                     order by MostRecentlyValid.ValidFrom desc)

This assumes that ValidTo can also be null to indicate no end date. If ValidTo can't be null then you can remove the or condition. This also assumes a record is valid through the end of the day of the ValidTo date. If the record becomes old at the beginning of the day of the ValidTo date change >= to just >.

This worked for the handful and test data I tried it on but I'm fairly certain it'll work for all cases.

As for as efficiency, I'm not a SQL expert so I really don't know if this is the most efficient solution.

To join to another table you could do something like this

select  *
from    (select *
         from  t1
         where VersionId = (select  top 1 VersionId
                from  t1 as MostRecentlyValid
                where MostRecentlyValid.ValidFrom <= '2014/2/11'
                      and (MostRecentlyValid.ValidTo >= '2014/2/1'
                           or MostRecentlyValid.ValidTo is null)
                      and t1.Id = MostRecentlyValid.Id
                      order by MostRecentlyValid.ValidFrom desc ) ) as SelectedRecords
         inner join t2
            on SelectedRecords.Id = t2.Id