How do you add a CONSTRAINT for a VARCHAR(10) column to checks the Date format as yyyy/mm/dd

Question

I have tried:
ALTER TABLE dbo.tablename
ADD CONSTRAINT DF_Date_format
check (SDate LIKE '%[1-2][0-9][0-9][0-9]/[0-1][0-9]/[0-3][0-9]%')
******But this does not work for VARCHAR data type ********
and
I also tried creating a function as shown below but I got an error when trying to add a constraint with this function.
(error is:
'The ALTER TABLE statement conflicted with the CHECK constraint "DF_Date_format". The conflict occurred in database " databasename ", table "dbo.tablename", column 'Date'.)
Create FUNCTION [dbo].[CheckDateFormat]
(@Date varchar(10))
Returns BIT
AS
BEGIN
Declare @RETURN BIT
SELECT @Return =
Case when (substring (@Date, 5, 1) + substring (@Date, 8, 1)) = '//'
then 0
else 1
end
Return @Return
END
ALTER TABLE dbo.tablename
ADD CONSTRAINT DF_Date_format
check
( dbo.CheckDateFormat(SDate) = 0 )

Answer 1

As noted above, be mindful of the performance implications of UDF CHECK constraints:
http://www.sqlusa.com/bestpractices/udf-check-constraint/
The following logic works:
Create FUNCTION [dbo].[CheckDateFormat]
(@Date varchar(10))
Returns BIT
AS
BEGIN
Declare @RETURN BIT
SELECT @Return =
Case when (substring (@Date, 5, 1) + substring (@Date, 8, 1)) = '//'
then 0
else 1
end
Return @Return
END
GO
CREATE TABLE Orders (ID INT IDENTITY(1,1),
OrderDate varchar(10),
Amount money
GO
ALTER TABLE Orders
ADD CONSTRAINT DF_Date_format
check
( dbo.CheckDateFormat(OrderDate) = 0 )
GO
As noted above, DATE is a better choice for column data type.
Kalman Toth Database & OLAP Architect
SELECT Video Tutorials 4 Hours
New Book / Kindle: Exam 70-461 Bootcamp: Querying Microsoft SQL Server 2012