Why is SQL Server losing a millisecond?

Dan_Howard_53069 0
Viewed 33789

I have a table structured like this:

CREATE TABLE [TESTTABLE]
(
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [DateField] [datetime] NULL,
    [StringField] [varchar](50),
    [IntField] [int] NULL,
    [BitField] [bit] NULL
)

I execute the following code:

BEGIN 
   INSERT INTO TESTTABLE (IntField, BitField, StringField, DateField) 
   VALUES ('1', 1, 'hello', {ts '2009-04-03 15:41:27.378'});  

   SELECT SCOPE_IDENTITY()  
END

And then 

select * from testtable with (NOLOCK)

and my result shows:

2009-04-03 15:41:27.*377*

for the DateField column.

Any ideas why I seem to be losing a millisecond??

sql-server sql
6 Answers

SQL Server only stores time to approximately 1/300th of a second. These always fall on the 0, 3 and 7 milliseconds. E.g. counting up from 0 in the smallest increment:

00:00:00.000
00:00:00.003
00:00:00.007
00:00:00.010
00:00:00.013
...

If you need that millisecond accuracy, there's no pleasant way around it. The best options I've seen are to store the value in custom number fields and rebuild it every time you fetch the value, or to store it as a string of a known format. You can then (optionally) store an 'approximate' date in the native date type for the sake of speed, but it introduces a conceptual complexity that often isn't wanted.

Whatsit_552450
user_767400
user_313260

SQL Server is only accurate to 1/300th of a second. It will round values to the nearest 1/300th.

Tom_H_56966080

DATETIME does not have infinite precision - you are probably using a value that cannot accurately be represented with the available bits.

Admin1

SQL Server stores datetime values to a precision of 3 milliseconds. (I've heard about this, but can't find an official reference.)

bdukes_26880
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