DateTime2 vs. DateTime in SQL Server: Which Data Type Should You Choose?

SQL Server date and time type selection: Best practices for DateTime2 and DateTime

Understanding the difference between the datetime and datetime2 data types is critical when storing date and time information in SQL Server 2008 and later. Both types have their pros and cons, but Microsoft's advice is clear: for new apps, datetime2 is the first choice.

Feature comparison

• Precision: datetime2 allows a wider range of fractional seconds precision, from 0 to 7 decimal places. And datetime is limited to 3 decimal places.
• Storage: While datetime2 provides greater precision, it may use less storage than datetime when using user-specified precision.

MSDN Recommendations

MSDN’s official documentation on datetime strongly recommends using datetime2 in new applications:

<code>对于新项目，请使用 time、date、datetime2 和 datetimeoffset 数据类型。这些类型与 SQL 标准一致，更具可移植性。time、datetime2 和 datetimeoffset 提供更高的秒精度。datetimeoffset 为全球部署的应用程序提供时区支持。</code>

Advantages of DateTime2

• Larger date range: DateTime2 supports the range from -9999-12-31 to 9999-12-31, while datetime is limited to the range 1900-01-01 to 2079-06-06.
• Decimal precision: You can specify precision up to 7 decimal places, allowing for finer representation of time intervals.
• Storage efficiency: When using decimal precision, datetime2 may use less storage than datetime.
• Supports time zone offsets: The datetimeoffset type is a variant of datetime2 that allows you to store times with time zone offsets, which is useful for applications that span multiple time zones.

When to use DateTime

Although datetime2 is recommended for most applications, there are some situations where datetime is still preferable:

• Data legacy: If you are dealing with a legacy system or database that relies on datetime, migrating to datetime2 may not be practical.
• Compatibility with older versions of SQL Server: DateTime Backwards compatible with older versions of SQL Server, which you may need if you need to support those versions.

In general, the best practice is to use datetime2 for all new applications and, where possible, consider migrating older applications to datetime2 to take advantage of its superior features and performance.

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