Sean Lange (4/2/2013)
The biggest take away from this is that you should ALWAYS use the datetime datatype for datetime values. Using a varchar for dates just doesn't make sense. You don't store numbers in a varchar, I don't know why so many people store dates in a varchar.
That's true when STORING a date after it's been validated. But there have been many times when I had "dates" as input from a spreadsheet import or a form post that are strings. When using a "date" in a parameter, unless the source is a datetime datatyped column I set the parameter datatype to varchar or nvarchar. I really don't trust my inputs so I run the alleged "date" through a validator function that will reject non-dates and convert those that pass to whatever datetime datatype I need. This keeps non-date "dates" from causing run time errors.
Here's a date validation procedure I use. I wish I could turn it into a TVF, but the procedure depends on TRY...CATCH and that won't work. This is the surest way I've found to validate dates: by trying to convert them to a date datatype and rejecting those "dates" that won't convert. Depending on the desired date format (DMY vs YMD for example) a particular date might pass or fail this test while ISDATE might return true and give a false positive. In this procedure I'm using SMALLDATETIME as my conversion type and that can be changed to whatever datatype is required.
CREATE PROCEDURE [dbo].[IsValidDate]
@sDate VARCHAR(50)
,@sDateFormat CHAR(3) = 'DMY' -- MDY, DMY, YMD, YDM, MYD, DYM
AS
BEGIN
SET NOCOUNT ON
SET DATEFORMAT @sDateFormat
DECLARE
@dStdDate SMALLDATETIME
,@dUMCDate DATETIMEOFFSET
,@bIsValidUMCDate BIT
,@bIsValidDate BIT
SET @dStdDate = NULL
SET @dUMCDate = NULL
/* Check to see if this is a valid UMC date */
IF OBJECT_ID('tempdb..#CheckUMCDate') IS NOT NULL
DROP TABLE #CheckUMCDate
CREATE TABLE #CheckUMCDate (
[ID] INT IDENTITY(1,1) NOT NULL,
[InputDate] VARCHAR(50) NULL,
[ConvertedDate] VARCHAR(50) NULL,
[IsValidUMCDate] BIT NULL
PRIMARY KEY (ID))
BEGIN TRY
INSERT INTO #CheckUMCDate
EXEC dbo.IsValidUMCDate @sDate
END TRY
BEGIN CATCH
INSERT INTO #CheckUMCDate
SELECT
@sDate AS InputDate
,NULL ConvertedDate
,0 AS IsValidUMCDate
END CATCH
SELECT
@dUMCDate = ConvertedDate
,@bIsValidUMCDate = IsValidUMCDate
FROM
#CheckUMCDate
/* Check using regular SMALLDATETIME datatype */
BEGIN TRY
SET @dStdDate = CONVERT(SMALLDATETIME,@sDate)
SET @bIsValidDate = 1
END TRY
BEGIN CATCH
SET @bIsValidDate = 0
SET @dStdDate = NULL
END CATCH
SELECT
@sDate AS InputDate
,@dStdDate AS StdDate
,@bIsValidDate AS IsValidDate
,@dUMCDate AS UMCDate
,@bIsValidUMCDate AS IsValidUMCDate
/*
EXAMPLES:
EXEC dbo.IsValidDate '01-07-2001' -- Valid date
EXEC dbo.IsValidDate '1/7/2001' -- Valid date
EXEC dbo.IsValidDate '07-01-2001' -- Valid date
EXEC dbo.IsValidDate '7/1/2001' -- Valid date
EXEC dbo.IsValidDate '29-12-2013','DMY' -- Valid date in DMY format
EXEC dbo.IsValidDate '29-12-2013','MDY' -- Invalid date in MDY format
EXEC dbo.IsValidDate '32-12-2013' -- ERROR: Date out of range
EXEC dbo.IsValidDate '29-02-2013' -- ERROR: Not a leap year
EXEC dbo.IsValidDate 'xyz' -- ERROR: Invalid date
EXEC dbo.IsValidDate '1234' -- Invalid std date/valid umc date
EXEC dbo.IsValidDate '2013-01-08 15:44:12' -- Valid date
EXEC dbo.IsValidDate '2013-01-08 15:44:12.000' -- Valid date
EXEC dbo.IsValidDate '2013-01-08 15:44:12.208' -- Valid date
EXEC dbo.IsValidDate '2013-01-08 15:44:12.2081606' -- Invalid std date/valid umc date
EXEC dbo.IsValidDate '2013-01-08 15:44:12.2081606 +05:30' -- Invalid std date/valid umc date
*/
END