Normalization of Year bringing nulls back - sql

Question

I have the following query:
SELECT DISTINCT
YEAR(DateRegistered) as Years,
Months.[MonthName],
COUNT(UserID)as totalReg
FROM
Months WITH(NOLOCK)
LEFT OUTER JOIN
UserProfile WITH(NOLOCK)
ON
Months.MonthID = MONTH(DateRegistered)
AND
DateRegistered > DATEADD(MONTH, -12,GETDATE())
GROUP BY YEAR(DateRegistered), Months.[MonthName]
ORDER BY Months.[MonthName]
As you can tell this will always bring back 12 months worth of data. As such it is working, although there is a bug with this method.
It creates Null values in months where there is no data, now the record should exist(whole point of the query) but Year field is bringing Nulls which is something I dont want.
Now I understand the problem is because there is no data, how is it supposed to know what year?
So my question is - is there any way to sort this out and replace the nulls? I suspect I will have to completely change my methodology.
**YEAR** **MONTH** **TOTAL**
2013 April 1
2013 August 1
NULL December 0
2013 February 8
2013 January 1
2013 July 1
NULL June 0
2013 March 4
NULL May 0
NULL November 0
NULL October 0
2012 September 3

Answer 1

If you want 12 months of data, then construct a list of numbers from 1 to 12 and use these as offsets with getdate():
with nums as (
select 12 as level union all
select level - 1
from nums
where level > 1
)
select YEAR(thedate) as Years,
Months.[MonthName],
COUNT(UserID) as totalReg
FROM (select DATEADD(MONTH, - nums.level, GETDATE()) as thedate
from nums
) mon12 left outer join
Months WITH (NOLOCK)
on month(mon12.thedate) = months.monthid left outer join
UserProfile WITH (NOLOCK)
ON Months.MonthID = MONTH(DateRegistered) and
DateRegistered > DATEADD(MONTH, -12, GETDATE())
GROUP BY YEAR(thedate), Months.[MonthName]
ORDER BY Months.[MonthName];
I find something strange about the query though. You are defining the span from the current date. However, you seem to be splitting the months themselves on calendar boundaries. I also find the table months to be awkward. Why aren't you just using the datename() and month() functions?

Answer 2

Try this out:
;With dates as (
Select DateName(Month, getdate()) as [Month],
DatePart(Year, getdate()) as [Year],
1 as Iteration
Union All
Select DateName(Month,DATEADD(MONTH, -Iteration, getdate())),
DatePart(Year,DATEADD(MONTH, -Iteration, getdate())),
Iteration + 1
from dates
where Iteration < 12
)
SELECT DISTINCT
d.Year,
d.Month as [MonthName],
COUNT(up.UserID)as totalReg
FROM dates d
LEFT OUTER JOIN UserProfile up ON d.Month = DateName(DateRegistered)
And d.Year = DatePart(Year, DateRegistered)
GROUP BY d.Year, d.Month
ORDER BY d.Year, d.Month

Answer 3

Here's my attempt at a solution:
declare #UserProfile table
(
id bigint not null identity(1,1) primary key clustered
, name nvarchar(32) not null
, dateRegistered datetime not null default(getutcdate())
)
insert #UserProfile
select 'person 1', '2011-01-23'
union select 'person 2', '2013-01-01'
union select 'person 3', '2013-05-27'
declare #yearMin int, #yearMax int
select #yearMin = year(MIN(dateRegistered))
, #yearMax= year(MAX(dateRegistered))
from #UserProfile
;with monthCte as
(
select 1 monthNo, DATENAME(month, '1900-01-01') Name
union all
select monthNo + 1, DATENAME(month, dateadd(month,monthNo,'1900-01-01'))
from monthCte
where monthNo < 12
)
, yearCte as
(
select #yearMin yearNo
union all
select yearNo + 1
from yearCte
where yearNo < #yearMax
)
select y.yearNo, m.Name, COUNT(up.id) UsersRegisteredThisPeriod
from yearCte y
cross join monthCte m
left outer join #UserProfile up
on year(up.dateRegistered) = y.yearNo
and month(up.dateRegistered) = m.monthNo
group by y.yearNo, m.monthNo, m.Name
order by y.yearNo, m.monthNo
SQL Fiddle Version: http://sqlfiddle.com/#!6/d41d8/6640

Answer 4

You have to calculate the counts in a Derived Table (or a CTE) first and then join
untested:
SELECT
COALESCE(dt.Years, YEAR(DATEADD(MONTH, -Months.MonthID, GETDATE()))),
Months.[MonthName],
COALESCE(dt.totalReg, 0)
FROM
Months WITH(NOLOCK)
LEFT OUTER JOIN
(
SELECT
YEAR(DateRegistered) AS Years,
MONTH(DateRegistered) AS Mon,
COUNT(UserID)AS totalReg
FROM UserProfile WITH(NOLOCK)
WHERE DateRegistered > DATEADD(MONTH, -12,GETDATE())
GROUP BY
YEAR(DateRegistered),
MONTH(DateRegistered)
) AS dt
ON Months.MonthID = dt.mon
ORDER BY 1, Months.MonthID
I changed the order to Months.MonthID instead of MonthName and i added year because you might have august 2012 and 2013 in your result.