This article contains examples of converting a datetime value to a datetime2 value in SQL Server.
When you convert a datetime value to datetime2, the resulting value will depend on the fractional seconds precision that you assign to datetime2.
The datetime data type has a maximum of 3 digits for its fractional seconds part. Its accuracy is rounded to increments of .000, .003, or .007 seconds.
The datetime2 data type, on the other hand, allows you to specify a fractional seconds precision from 0 to 7. If you don’t specify this, it will use 7 (the default).