Generate calender

Question

How can I generate the dates for the entire range? Thanks

Answer 1

As Mitch Wheat suggests is his comment, probably the best way to improve the performance of this query is to use a numbers table in place of the recursive CTE used to generate the list of dates.

If you can't or won't use a numbers table, the performance of the date range CTE can be improved for large ranges using a method suggested by Itzik Ben-Gan:

DECLARE @t TABLE(startdate DATETIME , enddate DATETIME)
INSERT INTO @t 
    SELECT '8/01/2009','08/31/2009' UNION ALL
    SELECT '2/01/1900','02/28/1900' UNION ALL
    SELECT '10/01/1959','10/31/1959'

DECLARE @n INT
SET @n = DATEDIFF(dd,'19000201','20090831') + 1

;WITH base 
AS 
( 
        SELECT 1 AS n 
        UNION ALL 
        SELECT n+1 FROM base 
        WHERE n < CEILING(SQRT(@n)) 
) 
,cross_cte 
AS 
( 
        SELECT 0 AS c 
        FROM base AS b1 
        ,base AS b2 
) 
,dates_cte
AS
(
        SELECT TOP(@n) CAST('19000201' AS DATETIME) - 1 + ROW_NUMBER()  OVER(ORDER BY c) AS date
        FROM cross_cte 
)
SELECT DISTINCT d.DATE                  
FROM Dates_Cte d 
JOIN @t t 
ON d.DATE BETWEEN t.startdate AND t.enddate
OPTION ( MAXRECURSION 0);

Whilst the execution plan shows this version to be slightly less efficient than the original (=~ 1%), measuring with SET STATISTICS TIME on my system shows both the elapsed and CPU time for this version to be less than half that of yours.