Choosing Between DateTime and DateTime2 in SQL Server

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 than datetime.

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.