SQL to determine minimum sequential days of access?

Question

The following User History table contains one record for every day a given user has accessed a website (in a 24 hour UTC period). It has many thousands of r

Answer 1

How about one using Tally tables? It follows a more algorithmic approach, and execution plan is a breeze. Populate the tallyTable with numbers from 1 to 'MaxDaysBehind' that you want to scan the table (ie. 90 will look for 3 months behind,etc).

declare @ContinousDays int
set @ContinousDays = 30  -- select those that have 30 consecutive days

create table #tallyTable (Tally int)
insert into #tallyTable values (1)
...
insert into #tallyTable values (90) -- insert numbers for as many days behind as you want to scan

select [UserId],count(*),t.Tally from HistoryTable 
join #tallyTable as t on t.Tally>0
where [CreationDate]> getdate()-@ContinousDays-t.Tally and 
      [CreationDate]=@ContinousDays

delete #tallyTable