Understanding DateTime Backwards: Avoiding Regional Date/Time Issues in Microsoft SQL Server

SQL Server’s handling of dates and times can sometimes lead to confusion, particularly when working with string literals that represent combined date and time values. This article aims to explain the reasons behind these issues, how to identify the current session’s settings, and most importantly, how to avoid regional date/time problems when specifying such strings.

Background: Date/Time Formats in SQL Server

SQL Server does not store dates and times in a specific format; instead, it stores them as binary values. However, the interpretation of string literals and the output of dates as string literals depends on user options for date order and language. These settings are influenced by the session’s locale, which may differ from the one used to create the table.

Understanding Regional Date/Time Settings

To understand how SQL Server handles dates and times, it’s essential to grasp its regional date/time settings. Microsoft SQL Server Management Studio (SSMS) and other tools that interact with the database provide ways to inspect these settings.

Inspecting Current Session’s Date Format

One way to determine the current session’s date format is by using the dbcc useroptions query:

dbcc useroptions;

In the output, look for the value of the “dateformat” setting. This setting controls how dates are displayed and formatted in the database.

Inspecting Current Language

Another essential aspect to consider is the language assigned to your session. You can obtain this information using the following query:

select @@language;

This setting affects how numbers, currency symbols, and other elements are represented in the database and SSMS output.

The Issue: Different Formats for String Literals

When working with string literals that represent combined date and time values, it’s common to encounter issues. This can occur when specifying a value like '2019-02-28 20:11:38.980' or similar formats, which might be interpreted as valid but result in errors due to the regional settings.

The problem arises because SQL Server is not always able to distinguish between dates and times stored as binary values versus string literals represented in a specific format. This confusion can lead to incorrect conversions or comparisons of date/time values.

The Solution: Using Standard ISO 8601 Format

To avoid these issues, use the standard ISO 8601 format for combined date and time values:

YYYY-MM-DDThh:mm:ss

The “T” character in this format is a literal separator between date and time parts. This ensures that SQL Server can accurately interpret dates and times without being confused by regional settings.

For instance, using the convert function to parse a string literal into a datetime value:

select convert(datetime, '2019-02-28T20:11:38.980');

Additional Considerations

While the ISO 8601 format provides a standardized approach for representing combined date and time values in SQL Server, there are other considerations to keep in mind:

• Language Support: The standard ANSI Standard SQL date format “YYYY-MM-DD hh:mm:ss” is supposed to be multi-language. However, it does not work uniformly across all SQL languages (for example, Danish).
• Regional Variations: Even when using the ISO 8601 format, regional variations in month/day ordering can still cause issues.
• Session-Specific Settings: As mentioned earlier, session-specific settings for date order and language may affect how dates and times are interpreted.

Best Practices

To avoid these potential pitfalls:

• Use the standard ISO 8601 format when working with combined date and time values.
• Be mindful of regional variations and session-specific settings that might influence your date/time interpretations.
• Consider using the convert function to parse string literals into datetime values, ensuring accurate conversions across different locales.

Conclusion

When dealing with dates and times in Microsoft SQL Server, being aware of regional settings and format differences can significantly impact performance. By understanding how these settings interact and adopting best practices for representing combined date and time values using the ISO 8601 format, you’ll be better equipped to handle potential challenges and ensure accurate results.

Additional Resources

• Microsoft SQL Server Documentation: For detailed information on dates, times, and string literals in SQL Server.
• String Literal Date and Time Formats: Microsoft’s documentation on standard date formats for SQL Server string literals.
• Database Best Practices: To learn more about optimizing database performance and handling date/time differences.

Last modified on 2023-08-14