Update temp table with min datetime of multiple columns

Question

How can I update the following column "LowestFinishDate" in my #temp table to hold the absolute mininium value of columns ["Finished_OldDate", "Finished_NewDate" and "Current_FinishedDate"]?

This is what the table looks like for Parent0000:

So in this case I want all 7 rows in #temp.[LowestFinishDate] for Parent0000 to be updated to the lowest date which is:

2020-11-25 14:15.

I have tried doing a CROSS/OUTER APPLY and use a table-value constructor but for some reason each LowestFinishDate rows gets updated with the correspondent value of Current_FinishedDate.

Thanks in advance

Answer 1

In SQL Server, I would be inclined to write this as:

with toupdate as (
      select t.*,
             min(least_date) over (partition by t.parentid) as new_lowestfinishdate
      from #temp t cross apply
           (select min(dte) as least_date
            from (values (t.Finished_OldDate),
                         (t.Finished_NewDate)
                         (t.Current_FinishedDate)
                 ) v(dte)
           ) v
     )
update toudpate
    set lowestfinishdate = new_lowestfinishdate;

The cross apply takes the minimum value of the dates within each row. The window function then takes the minimum across all rows for the parent id.

Answer 2

One method is use use MIN with a subquery and a VALUES table construct:

UPDATE YT
SET LowestFinishedDate = (SELECT MIN(V.FinishDate)
                          FROM (VALUES (YT.FinishedOldDate),
                                       (YT.FinishedNewDate),
                                       (YT.CurrentFinishDate)) V(FinishDate)
                          WHERE V.FinishDate IS NOT NULL)
FROM dbo.YourTable;