SQL select, pad with chronological missing months - sql

Question

Notice the 2015-02 and 2015-03 months are missing in the output from the following group by SQL. If there is no data for a month I want to show the month and 0. Anyone know how to go about this?
SELECT convert(char(7), MeterReadDate, 121),count(*)
FROM [myTable]
where (MeterReadDate > dateadd(d,-356,getdate()))
group by convert(char(7), MeterReadDate, 121)
order by convert(char(7), MeterReadDate, 121)
Sample data:
YYYY-MM COUNT
2014-06 23
2014-07 42
2014-08 80
2014-09 92
2014-10 232
2014-11 88
2014-12 8
2015-01 5
2015-04 2
2015-05 1
Still cannot clear the missing rows, here is where I am with it..
DECLARE #StartDate DATETIME = dateadd(m,-12,getdate()), #EndDate DATETIME = getdate(), #DATE DATETIME
DECLARE #TEMP AS TABLE (MeterReadDate datetime)
SET #DATE = #StartDate
WHILE #DATE <= #EndDate
BEGIN
INSERT INTO #TEMP VALUES ( #DATE)
SET #DATE = DATEADD(MONTH,1,#DATE)
END
SELECT convert(char(7), t.MeterReadDate, 121),count(*)
FROM #TEMP m left join
[myTable] t
on convert(char(7), t.MeterReadDate, 121) = convert(char(7), m.MeterReadDate, 121)
where (t.MeterReadDate > dateadd(m,-12,getdate()))
group by convert(char(7), t.MeterReadDate, 121)
order by convert(char(7), t.MeterReadDate, 121)

Answer 1

If you don't want to go beyond your min and max dates of your results then you can do the following:
WITH cte
AS ( SELECT convert(char(7), MeterReadDate, 121) AS [Date], COUNT(*) AS [Count]
FROM [myTable]
WHERE (MeterReadDate > dateadd(d,-356,getdate()))
GROUP by convert(char(7), MeterReadDate, 121)
),
minmax
AS ( SELECT CAST(MIN([Date] + '-01') AS DATE) AS mind ,
CAST(MAX([Date] + '-01') AS DATE) maxd
FROM cte
),
calendar
AS ( SELECT mind ,
CONVERT(CHAR(7), mind, 121) AS cmind
FROM minmax
UNION ALL
SELECT DATEADD(mm, 1, calendar.mind) ,
CONVERT(CHAR(7), DATEADD(mm, 1, calendar.mind), 121)
FROM calendar
CROSS JOIN minmax
WHERE calendar.mind < minmax.maxd
)
SELECT c.cmind AS [Date],
ISNULL(cte.[Count], 0) AS [Count]
FROM calendar c
LEFT JOIN cte ON c.cmind = cte.[Date]
OPTION ( MAXRECURSION 0 )

Answer 2

You need a list of dates/months that covers the entire period. Here is one method using a recursive CTE:
with months as (
select cast(getdate() - 365) as thedate
union all
select date_add(1, month, thedate)
from months
where thedate <= getdate()
)
select convert(char(7), m.thedate, 121) as yyyy-mm, count(t.MeterReadDate)
from months m left join
[myTable] t
on convert(char(7), MeterReadDate, 121) = convert(char(7), m.thedate, 121)
group by convert(char(7), m.thedate, 121)
order by convert(char(7), m.thedate, 121);

Answer 3

The best way to do this would be to join onto a table containing calendar information, one way to do this without actually altering the database schema (and is more dynamic in my opinion) would be to use a table variable and the DATEADD() function.
DECLARE #StartDate DATETIME = '2015-01-01', #EndDate DATETIME = '2015-12-01', #DATE DATETIME
DECLARE #TEMP AS TABLE ([DATE] DATETIME)
SET #DATE = #StartDate
WHILE #DATE <= #EndDate
BEGIN
INSERT INTO #TEMP VALUES (#DATE)
SET #DATE = DATEADD(MONTH,1,#DATE)
END
SELECT * FROM #TEMP
Set #Start and #End to your required dates, then just join onto your results set!
UPDATE:
To extract the date in the format you gave above under "sample data", meaning you would be able to join onto the table, use:
SELECT
CONCAT(YEAR([DATE]),'-',right('0' + cast(month([DATE]) as varchar),2))
FROM #TEMP
LEFT JOIN MyTable ON...