Including default values on dynamic pivot - sql

Question

I am pivoting data in a table based on date, but need to return NULL for dates with no data.
Data in [dbo].[Metrics]:
The dynamic pivot SQL I am executing:
DECLARE #cols NVARCHAR(1000);
SELECT #cols =
STUFF((SELECT N'],[' + month_day
FROM (SELECT DISTINCT RIGHT(CONVERT(NCHAR(10), [Date], 126), 2)
FROM [Metrics]) AS O(month_day)
ORDER BY month_day
FOR XML PATH('')
), 1, 2, '') + N']';
DECLARE #sql NVARCHAR(2000);
SET #sql =
N'SELECT [Key], ' + #cols +
N' FROM (SELECT [Key], ' +
N' RIGHT(CONVERT(NCHAR(10), [Date], 126), 2) AS month_day, ' +
N' [Value] ' +
N' FROM [Metrics]) AS O ' +
N'PIVOT ' +
N'(SUM([Value]) FOR month_day IN (' + #cols + N')) AS P;';
EXECUTE(#sql);
...and the result set that dynamic SQL returns:
As you can see, since I do not have data for every day of the month it is simply not returning columns for those days. How can I have it return columns 10-23 and 28-31 with NULL for each cell? It should return columns 1-31 regardless of the actual month (e.g., 31 columns even when there are less than 31 days in a given month).
Any help is appreciated.

Answer 1

Then you don't really need that columns to be generated dynamically, since you always want them from 1 to 31. The easier way would be hardcoding those values on your pivot, really. Anyway, here is the way you can define your columns dynamically and still get all days:
SELECT #cols =
STUFF((SELECT N'],[' + CAST(number AS VARCHAR(2))
FROM (SELECT DISTINCT number
FROM master..[spt_values]
WHERE number BETWEEN 1 AND 31) AS O(number)
ORDER BY number
FOR XML PATH('')
), 1, 2, '') + N']';
And the version you really should be using is this:
SELECT *
FROM (SELECT [Key],
RIGHT(CONVERT(NCHAR(10), [Date], 126), 2) AS month_day,
[Value]
FROM [Metrics]) AS O
PIVOT (SUM([Value]) FOR month_day IN ([01],[02],[03],[04],[05],[06],[07],[08],[09],
[10],[11],[12],[13],[14],[15],[16],[17],[18],
[19],[20],[21],[22],[23],[24],[25],[26],[27],
[28],[29],[30],[31])) AS P;