Question

I have date that I want to increment with 1 millisecond. I am using this sql,

DECLARE @A TABLE
(
    A VARCHAR(2)
)
INSERT INTO @A(A) VALUES ('a1')
INSERT INTO @A(A) VALUES ('b2')
INSERT INTO @A(A) VALUES ('a3')
INSERT INTO @A(A) VALUES ('b4')
INSERT INTO @A(A) VALUES ('a5')
INSERT INTO @A(A) VALUES ('b6')
INSERT INTO @A(A) VALUES ('a7')
INSERT INTO @A(A) VALUES ('b8')

SELECT DATEADD(millisecond, + ROW_NUMBER() OVER (ORDER BY A), '2012-11-22     15:09:24.990'),ROW_NUMBER() OVER (ORDER BY A)
FROM @A

But the result is,

2012-11-22 15:09:24.990 1
2012-11-22 15:09:24.993 2
2012-11-22 15:09:24.993 3
2012-11-22 15:09:24.993 4
2012-11-22 15:09:24.997 5
2012-11-22 15:09:24.997 6
2012-11-22 15:09:24.997 7
2012-11-22 15:09:24.997 8

which is incorrect

Answer 1

The DATETIME datatype in SQL Server has a 3.33ms resolution.

You will never be able to create 15:09:24.991 and other values – what you’re seeing is expected and documented behavior.

If you need greater accuracy – use the DATETIME2 datatype instead (which can handle accuracy down to 100ns).

DECLARE @StartValue DATETIME2(3) = '20121122 15:09:24.990'

SELECT 
    @StartValue,
    DATEADD(Millisecond, 1, @StartValue),
    DATEADD(Millisecond, 2, @StartValue),
    DATEADD(Millisecond, 3, @StartValue)

generates results:

2012-11-22 15:09:24.990
2012-11-22 15:09:24.991
2012-11-22 15:09:24.992
2012-11-22 15:09:24.993

as you wanted.

Update: if you must stick with DATETIME – yes, you can add +3 and get these results:

DECLARE @StartValue DATETIME = '20121122 15:09:24.990'

SELECT 
    @StartValue, 
    DATEADD(Millisecond, 3, @StartValue),
    DATEADD(Millisecond, 6, @StartValue),
    DATEADD(Millisecond, 9, @StartValue)

gives you:

2012-11-22 15:09:24.990 
2012-11-22 15:09:24.993 
2012-11-22 15:09:24.997 
2012-11-22 15:09:25.000