In SQL Server, there are two commonly used data types for storing date and time values: datetime
and datetime2
. While both can be used to store temporal information, they have distinct differences in terms of range, precision, and storage requirements. In this tutorial, we will explore the characteristics of each data type and provide guidance on when to use them.
DateTime Data Type
The datetime
data type has been available since the early versions of SQL Server. It stores date and time values with a range of January 1, 1753, to December 31, 9999. The precision of datetime
is limited to 3 milliseconds (or 3 1/3 milliseconds), which can lead to rounding issues when storing or retrieving values.
Here’s an example of declaring a variable using the datetime
data type:
DECLARE @dt datetime = '2022-01-01 12:00:00.000';
DateTime2 Data Type
The datetime2
data type was introduced in SQL Server 2008 and provides several improvements over the traditional datetime
type. It has a larger date range, from January 1, 0001, to December 31, 9999, and offers higher precision, with accuracy up to 100 nanoseconds.
One of the key benefits of datetime2
is its ability to store fractional seconds with user-specified precision. The default precision is 7 digits, but you can specify a value between 0 and 7 to control the level of precision.
Here’s an example of declaring a variable using the datetime2
data type:
DECLARE @dt2 datetime2(3) = '2022-01-01 12:00:00.123';
In this example, the (3)
specifies that we want to store fractional seconds with 3 digits of precision.
Comparison and Recommendations
When deciding between datetime
and datetime2
, consider the following factors:
- Range: If you need to store dates outside the range of January 1, 1753, to December 31, 9999, use
datetime2
. - Precision: If you require higher precision than 3 milliseconds, use
datetime2
. - Storage: Depending on the specified precision,
datetime2
may use less storage space thandatetime
.
In general, it’s recommended to use datetime2
for new applications and projects, as it provides a more modern and flexible data type. However, if you’re working with legacy systems or need to maintain compatibility with older versions of SQL Server, datetime
might still be the better choice.
Additional Considerations
When mapping .NET DateTime
values to SQL Server data types, keep in mind that implicit rounding can occur when using the traditional datetime
type. This can lead to unexpected results and errors. To avoid these issues, use datetime2
whenever possible.
In summary, datetime2
offers a more robust and flexible data type for storing date and time values in SQL Server. Its larger range, higher precision, and user-specified fractional seconds make it the preferred choice for most applications.