SQL Server强制转换和转换DateTime和DateTime2失败

Question

Firstly, Here is some information about my environment:

I'm running a SQL 2005 database on a SQL 2014 instance. COLLATION is SQL_Latin1_General_CP1_CI_AS. Here are the results of my DBCC USEROPTIONS

• textsize 2147483647
• language us_english
• dateformat mdy
• datefirst 7
• lock_timeout -1
• quoted_identifier SET
• arithabort SET
• ansi_null_dflt_on SET
• ansi_warnings SET
• ansi_padding SET
• ansi_nulls SET
• concat_null_yields_null SET
• isolation level read committed

Here is my problem.

I keep running into the following 2 errors depending on when I try to select from a view and us a WHERE clause against a converted column of type DATETIME or DATETIME2.

(DATETIME2) Msg 241, Level 16, State 1, Line 122 Conversion failed when converting date and/or time from character string.

And...

(DATETIME) Msg 242, Level 16, State 3, Line 122 The conversion of a varchar data type to a datetime data type resulted in an out-of-range value.

My problem SOUNDS deceptively simple, like I must be a mook and am either passing in an incorrectly formatted value in the WHERE or not taking into account the language settings, collation, and optimizer precedence.

So here is my query.

DECLARE @DATEVALUE DATETIME = '01-05-2015 14:23:05'
SELECT t.* FROM Reports.MyReportView WHERE t.MyDateColumn = @DATEVALUE

This fails MISERABLY no matter what I try.

I have no problem casting and converting character strings to DATETIME. Like...

SELECT CAST('03/28/2011 18:03:40' AS DATETIME) 

Works just fine.

The problem only seems to happen in my WHERE clause. I've looked at tons of suggestions, tried lots of things such as changing the language settings to british or french, changing the DATEFORMAT to ymd, dmy, mdy, tried some other solutions I found such as...

DECLARE @F7 nvarchar(10) = '01/05/2015'
DECLARE @F8 nvarchar(10) = '00:00:00'
DECLARE @NEWTIME DATETIME

DECLARE @Date VARCHAR(20)
SET @Date = RIGHT(@F7,4)+'/'+SUBSTRING(@F7,4,2)+'/'+LEFT(@F7,2)

DECLARE @time DATETIME
SET @time =  CONVERT(DATETIME, @Date + ' ' + @F8) 

...And yes, that outputs a DATETIME just fine. But the moment I try to use the value in my WHERE clause ... KAAAABOOOOOOOM!!! So I've had no luck resolving this problem.

The only thing I can think of is that the optimizer is punking me because it's rearranging the query behind the scenes and I am comparing a VALID datetime variable to an invalid VARCHAR string PRIOR to when I am converting the string in the query order, and so it is the View that is actually causing the failure and has nothing to do with SQL Server's datetime conversions.

Please help.

UPDATE

Ok Fixed. I followed advice from everyone and rewrote the date conversion in the View into a SubQuery/SubView and then Joined it. Here is what the new conversion code looks like...

CONVERT(DATETIME,
CASE 
    WHEN   
    (
        CASE 
            WHEN REPLACE(ISNULL(t.DayCol,''),' ','') = '' 
            THEN NULL ELSE REPLACE(ISNULL(t.DayCol,''),' ','') END
    ) IS NULL
    OR 
        (
            CASE WHEN REPLACE(ISNULL(t.MonthCol,''),' ','') = '' 
            THEN NULL ELSE REPLACE(ISNULL(t.MonthCol,''),' ','') END
        ) IS NULL
    OR 
        (
            CASE WHEN REPLACE(ISNULL(t.YearCol,''),' ','') = '' 
            OR t.YearCol = 'NoSelection' 
            THEN NULL ELSE t.YearCol END
        ) IS NULL
    OR  
    ISDATE
    (
        CONCAT
            (
                RIGHT('0' +REPLACE(MonthCol,' ',''),2),'/',
                RIGHT('0' + REPLACE(t.DayCol,' ',''), 2),'/',
                REPLACE(YearCol,' ','')
            )
    ) = 0
    THEN NULL
    ELSE 
    CONCAT
    (
        RIGHT('0' +REPLACE(MonthCol,' ',''),2),'/',
        RIGHT('0' + REPLACE(t.MonthCol,' ',''), 2),'/',
        REPLACE(YearCol,' ','')
    )
END) as 'MyDateColumn'

This is embarassing code, but it works, solves the problem and is unfortunately necessary because somebody didn't want to store date values as date columns in a wacky database structure... so maybe it will help somebody who runs into this problem.

Answer 1

If your data column that you are converting from can contain nulls or possibly have invalid date data in it, then you are going to get this error. The SQL engine will try to do the CAST on all the potential data BEFORE it filters the data on the WHERE clause. What you need to do is do a subquery, and then select and cast against that:

SELECT CAST(a.StringField AS datetime) AS TheDate
FROM (
    SELECT a.* FROM MyTable WHERE StringField = '12/1/2014'
) a

OR:

SELECT CAST(a.StringField AS datetime) AS TheDate
FROM (
    SELECT a.* FROM MyTable WHERE ISDATE(StringField) = 1
) a
WHERE CAST(a.StringField as datetime) = '12/1/2014'