Question

Apologies for the terrible title, not really sure how to explain this without a sample:

I’m trying to return a column in a query that alternates between 0 and 1 as the hour of a datetime column over the result set changes. Does anybody have suggestions of a good way to do this?? OR how it could be done with CTEs

I started looking into using CTEs, but didn’t get very far and am hoping there’s an easier way. See below for a very basic example of what I’m hoping to achieve, with current output and the output I want. NOTE that I’ve created a column [band] that does what I want provided the times are all on the same day. Of course it breaks when then the dates cover more than one day.

declare @test as table(id int, dt datetime, comment varchar(50))

insert into @test values(1, '2011-01-01 07:00', 'one')
insert into @test values(2, '2011-01-01 07:30', 'two')
insert into @test values(3, '2011-01-02 07:50', 'three')
insert into @test values(4, '2011-01-03 08:00', 'four')
insert into @test values(5, '2011-01-03 08:50', 'five')
insert into @test values(6, '2011-01-03 09:00', 'six')
insert into @test values(7, '2011-01-03 10:00', 'seven');

select *, DATEPART(HOUR, dt) % 2 as [band]
from @test

CURRENT OUTPUT

1   2011-01-01 07:00:00.000 one     1
2   2011-01-01 07:30:00.000 two     1
3   2011-01-02 07:50:00.000 three   1
4   2011-01-03 08:00:00.000 four    0
5   2011-01-03 08:50:00.000 five    0
6   2011-01-03 09:00:00.000 six     1
7   2011-01-03 10:00:00.000 seven   0

REQUIRED OUTPUT

1   2011-01-01 07:00:00.000 one     1
2   2011-01-01 07:30:00.000 two     1
3   2011-01-02 07:50:00.000 three   0
4   2011-01-03 08:00:00.000 four    1
5   2011-01-03 08:50:00.000 five    1
6   2011-01-03 09:00:00.000 six     0
7   2011-01-03 10:00:00.000 seven   1

Note here that I want the [band] column to alternate as the datetime in the rows change to new hours. Whether they’re the next hour in the same day or another hour in the following day.

Answer 1

How about?

SELECT *, 
    (dense_rank() over (order by Dateadd(hh,Datediff(hh,0,dt),0))) % 2 as [band]
FROM @test

I don’t have sql at hand right now. But

1. The dateadd/datediff cleans the minutes off the hours
2. The dense_rank then orders them like rownumber but doesn’t number duplicates
3. then the %2 does what you were doing in your original query.