SQL Server DATE conversion error - sql

Question

Here is my query:
SELECT
*
FROM
(SELECT
A.Name, AP.PropertyName, APV.Value AS [PropertyValue],
CONVERT(DATETIME, APV.VALUE, 101) AS [DateValue]
FROM dbo.Account AS A
JOIN dbo.AccountProperty AS AP ON AP.AccountTypeId = A.AccountTypeId
JOIN dbo.AccountPropertyValue AS APV ON APV.AccountPropertyId = APV.AccountPropertyId
AND APV.AccountId = A.AccountId
WHERE
A.AccountTypeId = '19602AEF-27B2-46E6-A068-7E8C18B0DD75' --VENDOR
AND AP.PropertyName LIKE '%DATE%'
AND ISDATE(APV.Value) = 1
AND LEN(SUBSTRING( REVERSE(APV.Value), 0 , CHARINDEX( '/', REVERSE(APV.Value)))) = 4 --ENSURE 4 digit year
) AS APV
WHERE
APV.DateValue < GETDATE()
It results in the following error:
Conversion failed when converting date and/or time from character string.
If you comment out the WHERE APV.DateValue < GETDATE() clause then there is no error and I get the 300+ rows. When I enable the WHERE clause I get the error.
So you are going to tell me my data is jacked up right? Well that's what I thought, so I tried to figure out where the problem in the data was, so I started using TOP() to isolate the location. Problem was once I use the TOP() function the error went away, I only have 2000 rows of data to begin with. So I put a ridiculous TOP(99999999) on the inner SELECT and now the entire query works.
The inner SELECT returns the same number of rows with or without the TOP().
WHY???
FYI, this is SQL that works:
SELECT
*
FROM
(SELECT TOP(99999999)
A.Name, AP.PropertyName, APV.Value AS [PropertyValue],
CONVERT(DATETIME, APV.VALUE, 101) AS [DateValue]
FROM dbo.Account AS A
JOIN dbo.AccountProperty AS AP ON AP.AccountTypeId = A.AccountTypeId
JOIN dbo.AccountPropertyValue AS APV ON APV.AccountPropertyId = APV.AccountPropertyId
AND APV.AccountId = A.AccountId
WHERE
A.AccountTypeId = '19602AEF-27B2-46E6-A068-7E8C18B0DD75' --VENDOR
AND AP.PropertyName LIKE '%DATE%'
AND ISDATE(APV.Value) = 1
AND LEN(SUBSTRING(REVERSE(APV.Value), 0 , CHARINDEX( '/', REVERSE(APV.Value)))) = 4
) AS APV
WHERE
APV.DateValue < GETDATE()

Answer 1

The problem that you are facing is that SQL Server can evaluate the expressions at any time during the query processing -- even before the WHERE clause gets evaluated. This can be a big benefit for performance. But, the consequence is that errors can be generated by rows not in the final result set. (This is true of divide-by-zero as well as conversion errors.)
Fortunately, SQL Server has a work-around for the conversion problem. Use try_convert():
TRY_CONVERT( DATETIME, APV.VALUE, 101) AS [DateValue]
This returns NULL rather than an error if there is a problem.
The reason why some versions work and others don't is because of the order of execution. There really isn't a way to predict what does and does not work -- and it could change if the execution plan for the query changes for other reasons (such as table statistics). Hence, use try_convert().

Answer 2

My guess is that your date is such that APV.VALUE contains also data that cannot be converted into a date, and should be filtered out using the other criteria?
Since SQL Server can decide to limit the data first using the criteria you have given:
APV.DateValue < CONVERT( DATETIME, GETDATE(),101)
And if there is data that cannot be converted into the date, then you will get the error.
To make it more clear, this is what is being filtered:
CONVERT( DATETIME, APV.VALUE, 101) AS [DateValue]
And if there is any data that cannot be converted into a date using 101 format, the filter using getdate() will fail, even if the row would not be included in the final result set for example because AP.PropertyName does not contain DATE.
Since you're using SQL Server 2012, using try_convert instead of convert should fix your problem
And why it works with top? In that case SQL Server cannot use the criteria from the outer query, because then the result might change, because it might affect the number of rows returned by top

Answer 3

Because number of records in the table < 999..99. And regarding the error it seems like SQL engine evaluates the WHERE clause after converting to date so you can try this:
SELECT *
FROM (
SELECT A.Name
, AP.PropertyName
, APV.Value AS [PropertyValue]
,
CASE
WHEN SDATE(APV.Value) = 1
THEN CONVERT( DATETIME, APV.VALUE, 101)
ELSE NULL
END AS [DateValue]
FROM dbo.Account AS A
JOIN dbo.AccountProperty AS AP
ON AP.AccountTypeId = A.AccountTypeId
JOIN dbo.AccountPropertyValue AS APV
ON APV.AccountPropertyId = APV.AccountPropertyId
AND APV.AccountId = A.AccountId
WHERE A.AccountTypeId = '19602AEF-27B2-46E6-A068-7E8C18B0DD75' --VENDOR
AND AP.PropertyName LIKE '%DATE%'
AND LEN( SUBSTRING( REVERSE(APV.Value), 0 , CHARINDEX( '/', REVERSE(APV.Value)))) = 4 --ENSURE 4 digit year
) AS APV
WHERE APV.DateValue IS NOT NULL AND APV.DateValue < GETDATE()