Question

I wrote the following query to obtain a date, remove it’s time part and add the time I wanted.
If I run this query without the TOP clause, it works well. But when I add it, it returns the following exception: “Conversion failed when converting date and/or time from character string.”

Here is the query:

SELECT TOP 1 
CONVERT(DateTime, (CONVERT(varchar(50),CONVERT(Date, VRSAS.EventOn)) 
+ ' ' + 
CONVERT(varchar(50), CONVERT(Time, '23:30')))) E 
FROM ViewRangeSheetActualStatus VRSAS 
Where VRSAS.EventOn <= '2010-07-31' 
AND VRSAS.[Status] = 1
 order by VRSAS.RangeSheet

The field EventOn is of type DateTime.

What could be going on?

Answer 1

I’ve reproduced quite easily this end. I found using DATEADD resolved it

DATEADD(MINUTE, 23*60 + 30, CONVERT(DATETIME,CONVERT(DATE, VRSAS.EventOn)))

But I’m not actually sure why yet. Steps to reproduce below.

CREATE TABLE ViewRangeSheetActualStatus
(EventOn DATETIME,
[Status] BIT,
RangeSheet INT
)

INSERT INTO [dbo].[ViewRangeSheetActualStatus]([EventOn], [Status], [RangeSheet])
SELECT '20100903 11:02:39.517', 1, 1 UNION ALL
SELECT '20100731 11:03:23.577', 1, 1 UNION ALL
SELECT '20100731 00:00:00.000', 1, 1

/*Selects ALL records - No error*/
SELECT 
CONVERT(DateTime, (CONVERT(varchar(50),CONVERT(Date, VRSAS.EventOn)) 
+ ' ' + 
CONVERT(varchar(50), CONVERT(Time, '23:30')))) E 
FROM ViewRangeSheetActualStatus VRSAS 

/*Selects top (1) record - Error!*/   
SELECT top (1)
CONVERT(DateTime, (CONVERT(varchar(50),CONVERT(Date, VRSAS.EventOn)) 
+ ' ' + 
CONVERT(varchar(50), CONVERT(Time, '23:30')))) E 
FROM ViewRangeSheetActualStatus VRSAS 

Looking at the ComputeScalar properties in the execution plan the two are different.

All

(CONVERT(datetime,(CONVERT(varchar(50),CONVERT(date,[ViewRangeSheetActualStatus].
 [EventOn] as [VRSAS].[EventOn],0),0)+[@1])+CONVERT(varchar(50),CONVERT(time(7), 
 [@2],0),0),0))

Top 1

(CONVERT(datetime,(CONVERT(varchar(50),CONVERT(date,[ViewRangeSheetActualStatus].
 [EventOn] as [VRSAS].[EventOn],0),121)+' ')+'23:30:00.0000000',0))

Before the final conversion to datetime the first one produces a varchar containing the following

------------------------------
Sep  3 2010 11:30PM
Jul 31 2010 11:30PM
Jul 31 2010 11:30PM

The second version produces a varchar containing

------------------------------
2010-09-03 23:30:00.0000000

It is the .0000000 that causes the problem casting back to datetime. I have no idea why the addition of TOP to the query would cause this completely unrelated change in behaviour.