Result of Calculated Field as Criteria?

Question

I'm using CASE and CAST to convert a field to datetime format so that I can account for null field values
CASE
     WHEN ISDATE([Date])=0 THEN 01/01/1900
     ELSE
         CAST([Date] as datetime)
END as [DateConverted]
How can I use this new [DateConverted] field in the criteria of my query so that I can only get records in a specific date range?

Answer 1

I prefer using the below approach for date range comparison
DECLARE @tmp TABLE (Id INT IDENTITY(1,1),[Date] VARCHAR(20))
INSERT @tmp SELECT 0
INSERT @tmp SELECT GETDATE()-1
INSERT @tmp SELECT GETDATE()
INSERT @tmp SELECT GETDATE()+1
--SELECT * FROM @tmp
SELECT * FROM (
SELECT Id,CASE
WHEN ISDATE([Date])=0 THEN 01/01/1900
ELSE CAST([Date] AS DATETIME)
END [DateConverted]
FROM @tmp ) tmp
WHERE [DateConverted] >='1900-01-01'
AND [DateConverted] <'2014-01-05'
Reason being there's a small chance of some records getting wrongly excluded/included when you use BETWEEN clause especially when datetime field stores time part also.
http://visakhm.blogspot.in/2012/12/different-ways-to-implement-date-range.html
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