IsDate() function returns wrong results

Question

IsDate() function returns wrong results

seaport

SSCrazy

Points: 2491
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April 8, 2015 at 9:36 am

#316418

All dates in codes below are valid dates, at least for me. But SQL identifies as not date, although some dates works for the Convert function.
SELECT isdate('04/01/200'), isdate('04/01/0200'), isdate('200-04-01'),isdate('0200-04-01'), ISDATE('01/01/0001')
--select convert(date,'04/01/200') -- error
select convert(date,'04/01/0200')
--select convert(date,'200-04-01') -- error
select convert(date,'0200-04-01')
Anyone knows the limitation of the IsDate function?
I got the same results in SQL 2008R2 and 2014.

Viewing 6 posts - 1 through 6 (of 6 total)

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Sean Lange SSC Guru Points: 286602 More actions · Answer 1

I suspect this is because the ISDATE function has been around since before we had the date datatype and the values you posted here are not valid as datetime. Once the date datatype came around we could get dates earlier than 1753. I am guessing that the ISDATE function didn't get updated. You will notice that it is unable to convert those values to datetime which I am guessing is what is happening behind the scenes in that function.

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Lowell SSC Guru Points: 323522 More actions · Answer 2

the two values you posted will convert to datetime2, but not date or datetime; maybe that's it?

--select convert(date,'04/01/200') -- error

select convert(datetime2,'04/01/0200')

--select convert(date,'200-04-01') -- error

select convert(datetime2,'0200-04-01')

Lowell

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Sean Lange SSC Guru Points: 286602 More actions · Answer 3

Lowell (4/8/2015)
the two values you posted will convert to datetime2, but not date or datetime; maybe that's it?
--select convert(date,'04/01/200') -- error
select convert(datetime2,'04/01/0200')
--select convert(date,'200-04-01') -- error
select convert(datetime2,'0200-04-01')

They both cast to date just fine on 2008r2.

--select convert(date,'04/01/200') -- error

select convert(date,'04/01/0200')

--select convert(date,'200-04-01') -- error

select convert(date,'0200-04-01')

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seaport SSCrazy Points: 2491 More actions · Answer 4

Sean Lange (4/8/2015)
I suspect this is because the ISDATE function has been around since before we had the date datatype and the values you posted here are not valid as datetime. Once the date datatype came around we could get dates earlier than 1753. I am guessing that the ISDATE function didn't get updated. You will notice that it is unable to convert those values to datetime which I am guessing is what is happening behind the scenes in that function.

Sean,

Great post. Following your lead I found that 1/1/1753 might be used as the minimum date in the IsDate(). Any date before that date is considered "Not Date". Check out the code below.

[Code]

SELECT isdate('01/01/1753'), isdate('12/31/1752')

[/Code]

Here is some interesting reading.

http://stackoverflow.com/questions/3310569/what-is-the-significance-of-1-1-1753-in-sql-server

seaport SSCrazy Points: 2491 More actions · Answer 5

I might have confused others with the code below. Its purpose is to show that SQL Convert function can handle date in Year 200, while ISDATE function cannot.

select convert(date,'04/01/0200')

select convert(date,'0200-04-01')

IsDate() function returns wrong results

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