Question

I have 2 tables: t1 and t2.

• a date column on t1 which is defined as DateTime2(3)
• a date column on t2 which is defined as DateTime

I am trying to get the value of Date column from t1 and use it to update the Date on t2.

Problem:

When

t1.Date = '2011-07-23 14:01:32.114'

and when I use this value to update t1.Date (which is DateTime) the update statement sets it to:

2011-07-23 14:01:32.113

which is 1 MILISECONDS lower.

Question:

How can I prevent/enforce this update so that SQL casts 2011-07-23 14:01:32.114 value coming from a DateTime2(3) type column again to 2011-07-23 14:01:32.114 so that I do not have that 1 MILISECOND difference on the other table?

Answer 1

In a nutshell, you can’t. DateTime2 has a larger fractional precision than DateTime does.

Why don’t you just alter table1 to use DateTime2 instead of DateTime?

From MSDN

Use the time, date, datetime2 and datetimeoffset data types for new
work. These types align with the SQL Standard. They are more portable.
time, datetime2 and datetimeoffset provide more seconds precision.
datetimeoffset provides time zone support for globally deployed
applications.

and

datetime values are rounded to increments of .000, .003, or .007
seconds