SQL DATEDIFF Function Use and Examples

Overview

The DATEDIFF function returns the difference between two dates according to the datepart specified: such as year, day, month, etc.

Explanation

Syntax

DATEDIFF(datepart, date1, date2)

Parameters

• datepart – This is the datepart to get the difference between the two dates. It can be a year (yy, yyyy), quarter (qq, q), month (mm, m), dayofyear(dy, y), day (dd, d), week (wk, ww), weekday (dw, w), hour (hh), minute (mi, n), second (ss, s), millisecond (ms), microsecond (mcs), nanosecond (ns). You can use the full name or the abbreviations in parenthesis.
• date1– Is the first date in the operation. This value can be a date or time.
• date2– Is the second date we want to use to compare with the first date. This value can be a date or time.

Simple DATEDIFF Example

The following example will show the number of years using the current date and March 11, 1979. If the dates were reversed, we would get a negative value.

SELECT DATEDIFF(year, '03-11-1979', CURRENT_TIMESTAMP) as yeardiff

Something to note is that DATEDIFF for year only takes the year part into consideration which was pointed out by one of the readers. So if we look at the example below this still returns 1, even though it has been less than 1 full year.

SELECT DATEDIFF(year, '02-01-2021', '01-01-2022') as yeardiff

DATEDIFF with NULL Values

If a NULL parameter is used the result will be NULL.

SELECT DATEDIFF(s, NULL, CURRENT_TIMESTAMP) as datediff

DATEDIFF Examples Using All Options

The next example will show the differences between two dates for each specific datapart and abbreviation. We will use the below date for the examples.

DECLARE @date  datetime2 = '2021-01-07 14:36:17.6222691'
DECLARE @date2 datetime2 = '2022-01-14 12:32:07.8494441'

Note: for the items that were left blank created an overflow error as shown below.

DATEDIFF Function Resulted in an Overflow

The following example will display an error message.

SELECT DATEDIFF(millisecond, '02-11-1972', CURRENT_TIMESTAMP) as datediff, 'millisecond' as unit 

The error message is the following:

The datediff function resulted in an overflow. The number of dateparts separating two date/time instances is too large. Try to use datediff with a less precise datepart.

This error occurs because there are too many milliseconds between 1972 until the current date.

Working with Table Data

The following example will show the number of years that the employee worked in a company based on the HireDate and they have worked there at least 10 years.

SELECT DATEDIFF(yy, HireDate, GETDATE()) as YEARS, BusinessEntityID
FROM HumanResources.Employee
WHERE DATEDIFF(yy, HireDate, GETDATE()) > 10

Additional Information

• SQL DATEADD
• How to Get Current Date in SQL Server
• Mimic timestamp behavior of other database platforms to store last modified date
• SQL Convert Date to YYYYMMDD