Question

my first time posting.

I have a tricky task of finding the latest date within a range, but excluding multiple other date ranges. I have code that does work, but it seems awfully taxing.

I am selecting the MAX(Date) within a range. However, I have a table, bfShow, where each show has its own date-range (stored as DateStart and DateEnd). So I need the MAX(Date) within the range which does NOT have a show on that date (there may be 0 to 99 shows overlapping my date-range).

Note: I have dbo.fnSeqDates which works great (found via Google) and returns all dates within a range – makes for very fast filling in 6/1/12, 6/2/12, 6/3/12…6/30/12, etc.

What I’m doing (below) is creating a table with all the dates (within range) in it, then find all the Shows within that range (#ShowIDs) and iterate through those shows, one at a time, deleting all those dates (from #DateRange). Ultimately, #DateRange is left with only “empty” dates. Thus, the MAX(Date) remaining in #DateRange is my last date in the month without a show.

Again, my code below does work, but there’s got to be a better way. Thoughts?

Thank you,
Todd

CREATE procedure spLastEmptyDate
    @DateStart date
  , @DateEnd   date
as
begin

   -- VARS...
   declare @ShowID    int
   declare @EmptyDate date

   -- TEMP TABLE...
   create table #DateRange(dDate date)
   create table #ShowIDs(ShowID int)

   -- LOAD ALL DATES IN RANGE (THIS MONTH-ISH)...
   insert into #DateRange(dDate)
   select SeqDate
   from dbo.fnSeqDates(@DateStart, @DateEnd)

   -- LOAD ALL SHOW IDs IN RANGE (THIS MONTH-IS)...
   insert into #ShowIDs(ShowID)
   select s.ShowID
   from bfShow s
   where s.DateStart = @DateStart

   -- PRIME SHOW ID...
   set @ShowID = 0
   select @ShowID = min(ShowID)
   from #ShowIDs

   -- RUN THRU ALL, REMOVING DATES AS WE GO...
   while (@ShowID > 0)
   begin
      -- REMOVE FROM TEMP...
      delete DR
      from #DateRange DR
         , bfShow s
      where DR.dDate between s.DateStart and s.DateEnd
        and s.ShowID = @ShowID

      -- DROP THAT ONE FROM TEMP...
      delete from #ShowIDs
      where ShowID = @ShowID

      -- GET NEXT ID...
      set @ShowID = 0
      select @ShowID = min(ShowID)
      from #ShowIDs
   end

   -- GET LAST EMPTY SPOT...
   select @EmptyDate = max(dDate)
   from #DateRange

   -- CLEAN UP...
   drop table #DateRange
   drop table #ShowIDs

   -- RETURN DATA...
   select @EmptyDate as LastEmptyDateInRange

end

Answer 1

Let us know what version of SQL Server you’re on because that will help determine your options, but you should be able to use the BETWEEN operator in a JOIN between the fnSeqDates function (it’s a table-valued function, so you can join to it directly rather than inserting them into a temp table) and the bfShow tables:

SELECT TOP 1 tDate.SeqDate
FROM dbo.fnSeqDates('6/1/2012', '6/30/2012') tDate
    LEFT JOIN bfShow tShow
        ON tDate.SeqDate BETWEEN tShow.DateStart AND tShow.DateEnd
WHERE tShow.ShowID IS NULL -- no matches found
ORDER BY tDate.SeqDate DESC -- to pull the most recent date