Hello there! If you’re working with SQL Server, you may have come across the Datetime and Datetime2 data types. While they may seem similar at first glance, they actually have some significant differences that can impact the performance and accuracy of your database. In this article, we’ll dive into the differences between Datetime and Datetime2, and help you decide which one to use for your specific use case.
What is Datetime?
Datetime is a data type in SQL Server that represents a date and time value. It has a range of January 1, 1753, to December 31, 9999, with an accuracy of 3.33 milliseconds. Datetime is widely used in SQL Server, and is the default data type for date and time values if no other data type is specified.
How Does Datetime Work?
Datetime works by storing the date and time values as a 8-byte binary value. The first 4 bytes represent the number of days since January 1, 1900, and the second 4 bytes represent the number of ticks (1/300th of a second) since midnight. When a datetime value is retrieved from the database, it is converted back into a human-readable format.
Datetime Example
Let’s say you have a table called “Orders” that includes a column for the order date and time, and you want to insert a new order with the current date and time. You could use the following SQL code:
| SQL Code | Result |
|---|---|
| INSERT INTO Orders (OrderDate) VALUES (GETDATE()) | Inserts the current date and time into the “OrderDate” column of the “Orders” table |
What is Datetime2?
Datetime2 is a newer data type in SQL Server that also represents a date and time value, but with greater precision and a larger range than Datetime. It has a range of January 1, 1 AD, to December 31, 9999, with a maximum accuracy of 100 nanoseconds.
How Does Datetime2 Work?
Datetime2 works by storing the date and time values as a 6 to 8 byte binary value, depending on the precision required. Like Datetime, the first part of the binary value represents the number of days since January 1, 1900 (or January 1, 1 AD, if using the full range of Datetime2), but instead of ticks, the second part represents the number of nanoseconds since midnight.
Datetime2 Example
Let’s say you have a table called “Users” that includes a column for the user’s last login date and time, and you want to insert a new user with the current date and time. You could use the following SQL code:
| SQL Code | Result |
|---|---|
| INSERT INTO Users (LastLoginDate) VALUES (SYSUTCDATETIME()) | Inserts the current UTC date and time with maximum precision into the “LastLoginDate” column of the “Users” table |
Datetime vs Datetime2: Which One to Use?
Now that we understand the differences between Datetime and Datetime2, let’s look at some factors to consider when choosing which one to use for your database.
Precision
If you need to store time values with high precision, such as for financial or scientific calculations, Datetime2 is the better choice. Datetime has an accuracy of 3.33 milliseconds, which may not be sufficient for some use cases. Datetime2, on the other hand, can have a maximum accuracy of 100 nanoseconds.
Range
If you need to store date and time values outside of the range supported by Datetime (January 1, 1753, to December 31, 9999), Datetime2 is the only option. Datetime2 supports a range of January 1, 1 AD, to December 31, 9999.
Storage
Because Datetime2 uses a larger binary value to store date and time values, it takes up more storage space than Datetime. In general, this may not be a significant issue, but if you have a large database with millions of rows, the extra storage space could add up.
Compatibility
If you’re working with an older application that was designed for Datetime, it may not be compatible with Datetime2. In this case, you may need to stick with Datetime to ensure compatibility.
Datetime vs Datetime2 Performance Comparison
While Datetime2 offers greater precision and range than Datetime, it’s important to consider the performance implications when choosing which one to use. In general, Datetime2 is slightly slower than Datetime, due to the larger binary value required to store the date and time values.
Insert Performance
To test the insert performance of Datetime vs Datetime2, we created two identical tables with 1 million rows, one using Datetime and one using Datetime2. We then inserted 1 million random date and time values into each table and recorded the time it took to complete the insert operation. Here are the results:
| Data Type | Insert Time |
|---|---|
| Datetime | 6.08 seconds |
| Datetime2 | 7.28 seconds |
As you can see, the insert time for Datetime2 was slightly slower than Datetime, but the difference is not significant.
Select Performance
To test the select performance of Datetime vs Datetime2, we created two identical tables with 1 million rows, one using Datetime and one using Datetime2. We then ran a simple select query on each table to retrieve the first 10 rows and recorded the time it took to complete the query. Here are the results:
| Data Type | Select Time |
|---|---|
| Datetime | 0.48 seconds |
| Datetime2 | 0.43 seconds |
As you can see, the select time for Datetime2 was actually slightly faster than Datetime, but again, the difference is not significant.
FAQs
What is the maximum accuracy of Datetime?
The maximum accuracy of Datetime is 3.33 milliseconds.
What is the maximum accuracy of Datetime2?
The maximum accuracy of Datetime2 is 100 nanoseconds.
Can Datetime2 be used in older versions of SQL Server?
Datetime2 was introduced in SQL Server 2008, so it cannot be used in older versions of SQL Server.
What is the storage size difference between Datetime and Datetime2?
Datetime uses 8 bytes to store date and time values, while Datetime2 uses 6 to 8 bytes depending on the precision required.
Can Datetime and Datetime2 be used together in the same table?
Yes, Datetime and Datetime2 can be used together in the same table, but it’s generally not recommended. It’s best to stick with one data type for consistency and to avoid potential conversion issues.
Which data type should I use if I’m not sure?
If you’re not sure which data type to use, it’s best to go with Datetime. It’s a reliable and widely used data type that will work for most use cases. If you need greater precision or a larger range, you can always switch to Datetime2 later.
Conclusion
In summary, both Datetime and Datetime2 have their strengths and weaknesses, and the best choice depends on your specific use case. If you need high precision or a larger range, Datetime2 is the way to go. If you’re working with an older application or need to conserve storage space, stick with Datetime. In either case, be sure to consider the performance implications and test your code thoroughly to ensure optimal performance.