Hello Dev, welcome to our journal article on SQL Server Date Difference. In this article, we will discuss how to calculate the difference between two dates using various methods in SQL Server.
Understanding Date and Time Datatypes
Before we dive into calculating date differences, let’s first understand the date and time datatypes available in SQL Server. SQL Server has two main datatypes for date and time: DATE and DATETIME.
The DATE datatype stores a date without a time component, while the DATETIME datatype stores both date and time information.
It’s essential to understand the datatype of the columns that you’re working with to ensure accurate date calculations.
DATE Datatype
The DATE datatype stores only the date component of a datetime value. It has a range of January 1, 0001, through December 31, 9999, with an accuracy of one day.
Here’s an example of a table with a DATE datatype column:
OrderID |
OrderDate |
OrderTotal |
|---|---|---|
1 |
2021-01-01 |
$100 |
2 |
2021-03-15 |
$200 |
3 |
2021-06-30 |
$150 |
In the above example, the OrderDate column stores only the date component of the order date. It’s essential to note that the time component of the datetime value is set to 00:00:00.
Now that we have a basic understanding of the DATE datatype, let’s move on to the DATETIME datatype.
DATETIME Datatype
The DATETIME datatype stores both date and time components of a value. It has a range of January 1, 1753, through December 31, 9999, with an accuracy of 3.33 milliseconds.
Here’s an example of a table with a DATETIME datatype column:
OrderID |
OrderDateTime |
OrderTotal |
|---|---|---|
1 |
2021-01-01 10:00:00 |
$100 |
2 |
2021-03-15 14:30:00 |
$200 |
3 |
2021-06-30 09:15:00 |
$150 |
In the above example, the OrderDateTime column stores both date and time components of the order date and time.
Calculating Date Difference using DATEDIFF Function
The most common way to calculate the difference between two dates in SQL Server is by using the DATEDIFF function. The DATEDIFF function returns the number of specified date parts between two dates.
Using DATEDIFF to Calculate Days Difference
Let’s use the above example of the Orders table to calculate the number of days between two orders.
To calculate the difference in days, we would use the following syntax:
SELECT OrderID, OrderDate, OrderTotal,DATEDIFF(day, OrderDate, '2021-06-30') AS 'DaysDifference'FROM Orders
The above query will return the number of days between the OrderDate column and the date ‘2021-06-30’. The DATEDIFF function takes three arguments: datepart, startdate, and enddate. In this case, we’re using ‘day’ as datepart and the OrderDate column as the startdate.
The result of the above query will be:
OrderID |
OrderDate |
OrderTotal |
DaysDifference |
|---|---|---|---|
1 |
2021-01-01 |
$100 |
180 |
2 |
2021-03-15 |
$200 |
107 |
3 |
2021-06-30 |
$150 |
0 |
The above query calculates the number of days between the OrderDate column and the date ‘2021-06-30’. As you can see, the DaysDifference column returns the number of days between each OrderDate and ‘2021-06-30’.
Using DATEDIFF to Calculate Months Difference
Similarly, you can use the DATEDIFF function to calculate the number of months between two dates. The syntax for calculating months difference is:
SELECT OrderID, OrderDate, OrderTotal,DATEDIFF(month, OrderDate, '2021-06-30') AS 'MonthsDifference'FROM Orders
The above query will return the number of months difference between the OrderDate column and the date ‘2021-06-30’. The DATEDIFF function takes three arguments: datepart, startdate, and enddate. In this case, we’re using ‘month’ as datepart and the OrderDate column as the startdate.
The result of the above query will be:
OrderID |
OrderDate |
OrderTotal |
MonthsDifference |
|---|---|---|---|
1 |
2021-01-01 |
$100 |
5 |
2 |
2021-03-15 |
$200 |
3 |
3 |
2021-06-30 |
$150 |
0 |
The above query calculates the number of months between the OrderDate column and the date ‘2021-06-30’. As you can see, the MonthsDifference column returns the number of months between each OrderDate and ‘2021-06-30’.
Calculating Date Difference using DATEDIFF_BIG Function
The DATEDIFF function has a limitation of 2,147,483,647 datepart differences. If you want to calculate date differences beyond this limit, you can use the DATEDIFF_BIG function.
The DATEDIFF_BIG function returns the number of specified date parts between two dates as a big integer. The syntax for using DATEDIFF_BIG is similar to DATEDIFF:
SELECT OrderID, OrderDateTime, OrderTotal,DATEDIFF_BIG(second, OrderDateTime, '2021-06-30 12:00:00') AS 'SecondsDifference'FROM OrdersDateTime
The above query will return the number of seconds between the OrderDateTime column and the datetime ‘2021-06-30 12:00:00’. The DATEDIFF_BIG function takes three arguments: datepart, startdate, and enddate. In this case, we’re using ‘second’ as datepart and the OrderDateTime column as the startdate.
The result of the above query will be:
OrderID |
OrderDateTime |
OrderTotal |
SecondsDifference |
|---|---|---|---|
1 |
2021-01-01 10:00:00 |
$100 |
15552000 |
2 |
2021-03-15 14:30:00 |
$200 |
8487600 |
3 |
2021-06-30 09:15:00 |
$150 |
-11700 |
The above query calculates the number of seconds between the OrderDateTime column and the datetime ‘2021-06-30 12:00:00’. As you can see, the SecondsDifference column returns the number of seconds between each OrderDateTime and ‘2021-06-30 12:00:00’.
Frequently Asked Questions (FAQ)
Q: Is it possible to calculate date differences using milliseconds?
A: Yes, you can use the DATEDIFF_BIG function with ‘millisecond’ as datepart to calculate date differences in milliseconds. Here’s an example:
SELECT DATEDIFF_BIG(millisecond, '2021-01-01 00:00:00', '2021-01-01 00:00:01')
The above query will return 1000, which is the number of milliseconds between the two dates.
Q: Can I use DATEDIFF to calculate date differences with decimal places?
A: No, the DATEDIFF function returns an integer value. If you need to calculate date differences with decimal places, you can calculate the difference in seconds or milliseconds using DATEDIFF_BIG and then divide the result by 1000 or 1000.0, respectively.
Q: Is there any difference between using DATE and DATETIME datatypes for date calculations?
A: Yes, there is a slight difference between using DATE and DATETIME datatypes for date calculations. When using the DATE datatype, the time component of the datetime value is set to 00:00:00, while using the DATETIME datatype stores both date and time components.
It’s essential to understand the datatype of the columns that you’re working with to ensure accurate date calculations.
Q: Can I use DATEDIFF to calculate date differences in different time zones?
A: No, DATEDIFF function calculates date differences based on the timezone of the server where SQL Server is running. To calculate date differences in different time zones, you should first convert the dates to UTC time and then use DATEDIFF.
Q: Can I use DATEDIFF to calculate date differences with non-standard date formats?
A: No, the DATEDIFF function only works with standard date formats. If you have non-standard date formats, you should first convert them to a standard format using the CONVERT function and then use DATEDIFF.
Conclusion
In this article, we discussed how to calculate the difference between two dates using various methods in SQL Server. We covered the DATE and DATETIME datatypes, the DATEDIFF function, and the DATEDIFF_BIG function.
It’s essential to understand the datatype of the columns that you’re working with to ensure accurate date calculations. We also answered some frequently asked questions regarding date calculations in SQL Server.
Now that you have a better understanding of how to calculate date differences in SQL Server, you can apply this knowledge to your own projects and queries to get more accurate results.