DateTime condition in where clause doesnt work correctly - sql

Question

I have row in my table with first column datetime type:
2021-11-01 08:51:56.123 102 296
When I use the select commands below, I get same result (this row):
select * from cmd where timestamp = convert(datetime, '2021-11-01 08:51:56.122')
select * from cmd where timestamp = convert(datetime, '2021-11-01 08:51:56.123')
select * from cmd where timestamp = convert(datetime, '2021-11-01 08:51:56.124')
I request that only the second command picks this line.
How to do it?
SQL Server is version 14

Answer 1

DATETIME has a precision of (about) .003 seconds. This means it can represent only every 3rd thousands of a second and everything else is rounded to increments of .000, .003, or .007 seconds, as shown in the following table.
User-specified value System stored value
01/01/98 23:59:59.999 1998-01-02 00:00:00.000
01/01/98 23:59:59.995
01/01/98 23:59:59.996
01/01/98 23:59:59.997
01/01/98 23:59:59.998 1998-01-01 23:59:59.997
01/01/98 23:59:59.992
01/01/98 23:59:59.993
01/01/98 23:59:59.994 1998-01-01 23:59:59.993
01/01/98 23:59:59.990
01/01/98 23:59:59.991 1998-01-01 23:59:59.990
You can use DATETIME2(3) instead of DATETIME for more precision.
For more details, please read https://learn.microsoft.com/en-us/sql/t-sql/data-types/datetime-transact-sql?view=sql-server-ver15