Use LEFT OUTER JOIN, but don't cast datetimes in any data table to dates to do comparisons; instead, use a range check.

Here's a sample join for the tables you've described:

SELECT ...

FROM dbo._dates d

INNER JOIN (

SELECT

DATEADD(DAY, DATEDIFF(DAY, 0, MIN(starttime)), 0) AS start_date,

DATEADD(DAY, DATEDIFF(DAY, 0, MAX(starttime)) + 1, 0) AS end_date

FROM dbo.cannedbackupjobs

) AS date_range ON

d.date >= date_range.start_date AND

d.date < date_range.end_date

LEFT OUTER JOIN cannedbackupjobs dbj ON

dbj.starttime >= d.date AND

dbj.starttime < DATEADD(DAY, 1, d.date)

--use the WHERE below instead of the INNER JOIN above if you want to

--report on just a specific date range that you specify

--WHERE d.date >= @start_date AND d.date < @end_date