SQL select, pad with chronological missing months

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 wan

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...