Understanding datetime vs datetimeoffset in T-SQL

Discover the key differences between `datetime`, `datetime2`, and `datetimeoffset` in T-SQL and how to choose the right one for your database needs.
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Understanding datetime vs datetimeoffset in T-SQL

In the world of SQL Server, managing date and time information is a common requirement, and choosing the right data type is critical for accurate data storage and manipulation. Three of the primary data types available for this purpose in T-SQL are datetime, datetime2, and datetimeoffset. This post aims to elucidate the differences among these types and help you make an informed choice for your database solutions.

datetime

The datetime data type in SQL Server has been around for a long time. It combines both date and time information into a single value. Here are some key characteristics:

Range: January 1, 1753, to December 31, 9999

Precision: Rounded to increments of .000, .003, or .007 seconds

Storage Size: 8 bytes

Typical Use Case: General purposes where historical data does not require high precision or timezone awareness.

datetime2

Introduced in SQL Server 2008, datetime2 is an enhanced version of the datetime data type. It provides greater precision and a larger date range. Some of its features include:

Range: January 1, 0001, to December 31, 9999

Precision: Up to 100 nanoseconds

Storage Size: 6 to 8 bytes, depending on the precision level used

Typical Use case: Scenarios requiring greater precision and smaller footprint compared to datetime.

datetimeoffset

datetimeoffset adds timezone awareness to the datetime2 data type. This allows the storage of date and time values including the timezone offset.

Range: January 1, 0001, to December 31, 9999

Precision: Up to 100 nanoseconds

Storage Size: 10 bytes

Timezone Offset: Timezone offset is stored in minutes

Typical Use Case: Systems requiring precise time calculations and timezone awareness, such as international applications and events logging.

Key Differences: datetime vs datetimeoffset

1. Timezone Awareness:

datetime: Lacks timezone information.

datetimeoffset: Includes timezone information.

2. Precision:

datetime: Rounded to increments of .000, .003, or .007 seconds.

datetimeoffset: Up to 100-nanosecond precision.

3. Storage Size:

datetime: 8 bytes.

datetimeoffset: 10 bytes.

When to Use Which?

Choosing among datetime, datetime2, and datetimeoffset largely depends on the specific needs of your application:

Use datetime if you don't need high precision or timezone information and if the data size is a concern.

Use datetime2 when you require high precision or have dates way back in history that fall outside the range of datetime.

Use datetimeoffset for applications needing timezone awareness and high precision, especially in distributed or international contexts.

Understanding these differences and their implications ensures you select the appropriate data type for accurate and efficient data storage and manipulation.