Learn how to format dates in SQL Server using the SQL FORMAT function and SQL CONVERT function. Explore various date formats and techniques 🛠
Converting Date Formats in SQL Server
Handling dates and times is an essential part of working with data in SQL Server. With global data sources, we often encounter datetimes in various formats. Having the flexibility to convert between formats is a crucial skill for T-SQL developers. In this comprehensive guide, we’ll explore the built-in SQL Server functions that allow you to reformat datetimes for your specific needs.
Why DateTime Conversions Matter in SQL Server
Let’s first understand why converting datetimes is so important in SQL Server.
At its core, SQL Server stores all datetime values in a internal unified format (datetime2). But the human-readable datetimes we see are formatted based on cultural standards.
For example, a date could be formatted as:
- mm/dd/yyyy – in the United States
- dd/mm/yyyy – in the United Kingdom
- yyyy-mm-dd – in Canada
Similarly, time formats vary across cultures:
- hh:mm:ss – 24-hour format
- hh:mm:ss am/pm – 12-hour format
To query, analyze and report on datetime data meaningfully, we need the ability to convert values into the right culture-specific formats.
Moreover, since datetime data comes from diverse sources into our SQL Server databases, they won’t always match the default format. We need functions to reformat them consistently.
Being able to convert datetimes also helps when exporting data to other systems. For example, another application may require dates in a specific format like ISO-8601 (yyyy-mm-dd).
In summary, some key reasons why datetime conversion matters:
- Display dates and times in culture-appropriate formats
- Standardize datetime values from diverse sources
- Enable integration with other systems needing specific formats
- Analyze and report on datetime fields meaningfully
- Handle time zones correctly for global datetime data
Using the SQL CONVERT Function to Change SQL Date Formats
The most common way to convert datetimes in T-SQL is using the CONVERT() function. This allows you to convert a datetime value into a specified format by using a format code.
For example, to convert a datetime into ‘dd/mm/yyyy’ format, you would use:
SELECT CONVERT(varchar(10), GETDATE(), 103)
Here we are converting the current datetime returned by GETDATE() into a varchar string with format code 103, which represents the ‘dd/mm/yyyy’ format.
Some other popular format codes for CONVERT() include:
- 101 – mm/dd/yyyy
- 102 – yyyy.mm.dd
- 110 – mm-dd-yyyy
- 120 – yyyy-mm-dd hh:mi:ss
So the CONVERT function allows you to easily reformat datetimes without worrying about the exact formatting strings. You just lookup the format code needed.
However, the codes do require some memorization. The CONVERT method also has a limited set of formats available. For more flexible formatting, SQL Server 2012 introduced the FORMAT function.
More Flexible Format Function Conversion with FORMAT()
The FORMAT() function provides greater flexibility for converting datetimes than CONVERT. With FORMAT(), you specify custom format strings rather than relying on format codes.
SELECT FORMAT(GETDATE(), 'dd/MM/yyyy')
This formats the current datetime into ‘dd/MM/yyyy’ format without needing a format code.
You can also use FORMAT() to convert datetimes into different cultures:
SELECT FORMAT(GETDATE(), 'D', 'de-DE')
This will format the current datetime into the German culture standard without having to lookup any german culture code.
Some common format strings used with FORMAT() include:
- ‘yyyy-MM-dd’ – ISO 8601 format
- ‘HH:mm:ss’ – Time only in 24-hour format
- ‘hh:mm tt’ – 12-hour time with AM/PM
- ‘MMM dd, yyyy’ – Month abbreviated name
With FORMAT(), you have much more control over the exact datetime format needed. Some other benefits include:
- No need to memorize format codes
- Culture conversions are simpler
- Flexible formatting for both date and time parts
- Customize formats to match other systems/reports
Overall, FORMAT() provides simpler, more customizable datetime conversions compared to CONVERT().
Handling Time Zones with AT TIME ZONE
When converting datetimes in SQL Server, you also need to consider time zones. SQL Server stores all datetimes internally in UTC format.
To convert datetimes from UTC to other time zones, SQL Server 2016 introduced the AT TIME ZONE function. For example:
SELECT GETDATE() AT TIME ZONE 'Eastern Standard Time'
This takes the current UTC datetime returned by GETDATE() and converts it to the Eastern Time zone.
Some common time zones used with AT TIME ZONE:
- ‘Pacific Standard Time’
- ‘Central European Standard Time’
- ‘Tokyo Standard Time’
- ‘New Zealand Standard Time’
By using AT TIME ZONE together with CONVERT or FORMAT, you can format datetimes appropriately for any time zone.
A few things to note about time zones in SQL Server:
- Time zones follow Daylight Saving Time rules for adjustments
- SQL Server does not automatically handle DST transitions
- You can use TODATETIMEOFFSET to explicitly handle DST
- The sys.time_zone_info view lists available time zones
Handling time zones is vital for global datetime data to represent values accurately per region.
Key Scenarios for DateTime Conversions in SQL Server
Now that we’ve covered the main datetime conversion functions, let’s discuss some real-world examples of how and when to use them.
Formatting Dates and Times for Reporting
A common need for datetime conversions is properly formatting values for reporting needs. For example, you may need to convert server date from the ISO standard ‘yyyy-mm-dd’ format stored in tables to a different format like ‘dd/MM/yyyy’ for a report.
Or when showing times, you may want to convert a 24-hour time like ’23:00:00′ to ’11:00:00 PM’ for reports viewed in the US.
The FORMAT and CONVERT functions help convert datetimes to matching culture and formatting needs for reporting.
Standardizing Datetimes from Different Sources
Another scenario is standardizing datetime values coming from diverse sources into your SQL Server database.
For instance, an externalCSV file may contain dates in ‘mm-dd-yyyy’ format. You need to convert them to match the ISO standard ‘yyyy-mm-dd’ format used in your tables.
Or a legacy application may insert datetimes in a non-standard ‘ dd-mm-yyyy ‘ format. You can use FORMAT() to convert those to a consistent format.
Having standardized datetimes simplifies queries and analysis.
Exporting Datetimes to Other Systems
You may also need to convert datetimes when exporting data from SQL Server to other systems and applications.
For example, an API request may require dates in yyyymmdd format without separators. Or a legacy application may need datetimes formatted in a special ‘dd mon yyyy hh:mm:ss’ format.
In such cases, use the CONVERT and FORMAT functions to transform datetimes into the exact formats required by external systems.
Converting Time Zones for Global Data
For global applications, converting between time zones is essential. If your SQL Server database contains data from multiple regions, use AT TIME ZONE to convert datetimes to the correct time zone.
This ensures dates and times align properly and are not misrepresented when querying, reporting or presenting data to users.
Adjusting for time zones is crucial to maintain data integrity with global datetime data.
Key Points for Datetime Conversion in SQL Server
Effectively handling datetime conversions in SQL Server is a crucial skill for database professionals. By mastering the following key pointers, you can ensure accurate and efficient manipulation of date and time data within your SQL queries:
- Utilize CONVERT() for Simple Formatting: When you need to perform basic datetime conversions, the CONVERT() function with format codes is your go-to tool. It allows you to easily change datetime data types, apply various formats, and manipulate the way dates and times are displayed.
- Leverage FORMAT() for Custom Conversions: For more complex conversions and custom string formatting, FORMAT() offers greater flexibility. This function enables you to create tailored date and time representations, making it invaluable for generating reports and user-friendly outputs.
- Handle Time Zones with AT TIME ZONE: Time zones can be a challenging aspect of datetime data. Use the AT TIME ZONE clause to ensure consistent and accurate handling of datetime data across different time zones. This is particularly important in scenarios involving international data or when dealing with data from various locations.
- Validate String Inputs for Safety: To prevent errors and potential security vulnerabilities, validate string inputs before performing datetime conversions. This step ensures that your SQL code remains robust and immune to unexpected input values.
- Optimize for Performance: When dealing with large volumes of datetime conversions, be mindful of performance. In such cases, consider indexing and proper data type selection, such as datetime2(n), which provides both precision and efficiency.
- Standardize Datetimes for Consistency: It’s essential to standardize datetimes from different sources to maintain consistency within your database. This involves converting them into a uniform format, which simplifies queries and reporting.
- Reformat Dates and Times for Reporting Needs: Adapt datetime values to meet reporting requirements. This might involve changing the format, rounding or truncating time components, or even aggregating data at specific intervals.
- Adjust Datetimes for Data Export: When exporting data to external systems or formats, ensure that datetimes are appropriately adjusted to match the target system’s expectations. This step helps maintain data integrity during transfers.
In summary, a solid grasp of datetime conversion functions and techniques in SQL Server empowers you to manipulate temporal data effectively. With regular practice, these skills become intuitive, allowing you to effortlessly transform datetimes from various sources into the desired format or time zone. Strengthening your datetime conversion expertise is essential for working efficiently with temporal data in SQL Server and ensuring the integrity of your database operations.