Insert Missing Dates from a query
Here is an example using a calendar table (which you really should have). This example just populates 2014 but you can stuff it with as many years as you like...

CREATE TABLE dbo.Calendar(d DATE PRIMARY KEY);

INSERT dbo.Calendar(d) SELECT TOP (365)
 DATEADD(DAY, ROW_NUMBER() OVER (ORDER BY number)-1, '20140101')
 FROM [master].dbo.spt_values
 WHERE [type] = N'P' ORDER BY number;


Now the query is simple:

DECLARE @s DATE = '20140518', @e DATE = '20140527';

SELECT c.d, Frequency = COALESCE(s.Frequency,0)
  FROM dbo.Calendar AS c
  LEFT OUTER JOIN dbo.splunge AS s
  ON c.d = s.[date]
  WHERE c.d &gt;= @s
    AND c.d &lt; DATEADD(DAY, 1, @e);


SQLfiddle example

If you can't create a calendar table (and don't have a numbers table handy either), then you can just put it inline:

DECLARE @s DATE = '20140518', @e DATE = '20140527';

SELECT c.d, Frequency = COALESCE(s.Frequency,0)
  FROM 
(
   SELECT TOP (DATEDIFF(DAY, @s, @e)+1)
 DATEADD(DAY, ROW_NUMBER() OVER (ORDER BY number)-1, @s)
 FROM [master].dbo.spt_values
 WHERE [type] = N'P' ORDER BY number
) AS c(d)
  LEFT OUTER JOIN dbo.splunge2 AS s
  ON c.d = s.[date]
  WHERE c.d &gt;= @s
    AND c.d &lt; DATEADD(DAY, 1, @e);


SQLfiddle example

For more on generating sets (of dates, numbers, etc) see this series:


http://sqlperformance.com/generate-a-set-1
http://sqlperformance.com/generate-a-set-2
http://sqlperformance.com/generate-a-set-3