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Let's learn everything you need to know about so-called “SQL Server date diff” operations to get the time difference between two dates.
Calculating the difference between two dates in SQL is common for tracking the duration of activities and measuring the time between two events. This operation, often informally referred to as “date diff,” enables precise time analysis to support data-driven decision-making. Not surprisingly, there are built-in SQL Server date diff functions to efficiently determine the intervals between date values in various time units.
In this article, you will dig into the date diff SQL Server approaches and learn how and when to use them.
Let’s dive in!
Calculating Date Difference in SQL Server
In SQL Server, calculating date difference refers to the process of determining the time interval between two date values. In simpler words, the idea is to get the difference between two dates in terms of years, months, days, hours, minutes, and/or seconds.
Keep in mind that the term “date difference” is frequently abbreviated to “date diff” for convenience, particularly in technical discussions and documentation. Therefore, we will henceforth refer to this operation as SQL Server date diff.
Whether it is referred to as one way or the other, the concept remains the same. In detail, date difference calculation represents a fundamental operation when working with dates in SQL Server across various scenarios.
For example, a business might need to analyze customer behavior by calculating the number of days between their first and last purchase. Similarly, a project manager might track the progress of a project by measuring the time difference between the start and end dates of tasks. Additionally, you may want to track the duration of events, measure the time elapsed between two transactions, or determine ages by calculating the difference between birthdates and the current date.
How to Perform SQL Server Date Diff
In SQL Server, there is only one recommended way to get the time between two date values. This is the DATEDIFF function, which has the following syntax:
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DATEDIFF(datepart, startdate, enddate)
The parameters accepted by this SQL Server function are:
DATEDIFF returns the count—as a signed integer value—of the specified datepart units passed between the startdate and enddate. If the startdate is greater than the enddate, the result will be a negative number.
Note that the supported SQL date data types for startdate and enddate are DATE, DATETIME, DATETIMEOFFSET, DATETIME2, SMALLDATETIME, TIME.
You can use the SQL Server DATEDIFF function as in the example below:
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SELECT
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DATEDIFF(YEAR, '2023-04-12', '2024-07-09') AS YearDifference,
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DATEDIFF(MONTH, '2023-04-12', '2024-07-09') AS MonthDifference,
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DATEDIFF(QUARTER, '2023-04-12', '2024-07-09') AS QuarterDifference,
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DATEDIFF(WEEK, '2023-04-12', '2024-07-09') AS WeekDifference,
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DATEDIFF(DAY, '2023-04-12', '2024-07-09') AS DayDifference;
Execute the query in SQL Server database client like DbVisualizer, and you will get:
For more information about this function, check out our guide on SQL DATEDIFF.
DATEDIFF is a powerful SQL Server function, but remembering the names of all possible datepart values is not easy. Fortunately, DbVisualizer comes with a full-featured SQL editor with advanced auto-complete capabilities:
Writing SQL queries has never been easier. Try DbVisualizer Pro via a free trial to test all its premium features, or download the free version today!
SQL Server Date Diff: Best Practices
Here are some SQL Server date diff best practices:
Conclusion
In this guide, you saw what date diff means and how the function is supported by SQL Server. You now know that DATEDIFF is an SQL Server function to get the time interval between two date values. Thanks to the best practices presented here, you also learned how to use it like a pro.
Dealing with date functions and formats becomes easier with a powerful client tool like DbVisualizer. This comprehensive database client supports several DBMS technologies, has advanced query optimization capabilities, and can generate ERD-type schemas with a single click. Try DbVisualizer for free!
FAQ
What does the “diff date” SQL Server expression stand for?
The “diff date” SQL Server expression typically stands for calculating the difference between two dates. This is an abbreviation of the “difference date” expression, which refers to the operation of returning the interval between two date values in specified units such as days, months, or years.
What data types do the SQL Server date diff functions support?
The SQL Server date diff functions DATEDIFF and DATEDIFF_BIG support the date and time formats below:
By default, both DATEDIFF and DATEDIFF_BIG casts string literals as a DATETIME2 type.
How to calculate the difference between two dates in SQL Server?
The simplest and most straightforward way to calculate the difference between two dates in SQL Server is to use the DATEDIFF function. This returns the difference in specified units of time, such as years, months, or days. For example:
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SELECT DATEDIFF(day, '2020-12-21', '2023-03-18');
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-- 817
To delve into the opposite of this operation, take a look at our guide on SQL add to date operations.
How to calculate the larger difference between two dates in SQL Server?
To calculate a larger difference between two dates in SQL Server, use the DATEDIFF_BIG function. Compared to DATEDIFF—which returns an INT—DATEDIFF_BIG returns a BIGINT result for greater precision. When it comes to syntax and usage, the two functions are the same.
Is it possible to subtract two dates in SQL Server with the subtraction operator?
No, you cannot directly subtract two dates using the subtraction operator. Try to write an SQL Server query like the one below:
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SELECT CAST('2023-04-12' AS DATE) - CAST('2024-07-09' AS DATE) AS DateDifference;
The result will be the following syntax error:
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[Code: 8117, SQL State: S1000] Operand data type date is invalid for subtract operator.
