Chapter 2: Transact-SQL Functions

datepart

Description

Returns the specified datepart in the first argument of the specified date (the second argument) as an integer. Takes a date, time, datetime, or smalldatetime value as its second argument. If the datepart is hour, minute, second, or millisecond, the result is 0.

Syntax

datepart(date_part, date expression)

Parameters

date_part

is a date part. Table 2-7 lists the date parts, the abbreviations recognized by datepart, and the acceptable values.

**Table 2-7: Date parts and their values**
Date part	Abbreviation	Values
year	yy	1753 – 9999 (2079 for smalldatetime). 0001 to 9999 for date
quarter	qq	1 – 4
month	mm	1 – 12
week	wk	1 – 54
day	dd	1 – 31
dayofyear	dy	1 – 366
weekday	dw	1 – 7 (Sun. – Sat.)
hour	hh	0 – 23
minute	mi	0 – 59
second	ss	0 – 59
millisecond	ms	0 – 999
calweekofyear	cwk	1 – 53
calyearofweek	cyr	1753 – 9999 (2079 for smalldatetime). 0001 to 9999 for date
caldayofweek	cdw	1 – 7

When you enter a year as two digits (yy):

Numbers less than 50 are interpreted as 20yy. For example, 01 is 2001, 32 is 2032, and 49 is 2049.
Numbers equal to or greater than 50 are interpreted as 19yy. For example, 50 is 1950, 74 is 1974, and 99 is 1999.

Milliseconds can be preceded by either a colon or a period. If preceded by a colon, the number means thousandths of a second. If preceded by a period, a single digit means tenths of a second, two digits mean hundredths of a second, and three digits mean thousandths of a second. For example, “12:30:20:1” means twenty and one-thousandth of a second past 12:30; “12:30:20.1” means twenty and one-tenth of a second past 12:30.

date expression: is an expression of type datetime, smalldatetime, date, time, or a character string in a datetime format.

Examples

Example 1

Assumes a current date of November 25, 1995:

select datepart(month, getdate())

-----------
          11

Example 2

Returns the year of publication from traditional cookbooks:

select datepart(year, pubdate) from titles where type = "trad_cook"

 -----------
        1990 
        1985 
        1987

Example 3

select datepart(cwk,’1993/01/01’)

-----------
          53

Example 4

select datepart(cyr,’1993/01/01’)

-----------
        1992

Example 5

select datepart(cdw,’1993/01/01’)

-----------
           5

Example 6

Find the hours in a time:

declare @a time
select @a = "20:43:22"
select datepart(hh, @a)
-----------
    20

Example 7

If a hour, minute, or second portion is requested from a date using datename or datepar) the result is the default time, zero. If a month, day, or year is requested from a time using datename or datepart, the result is the default date, Jan 1 1900:

--Find the hours in a date
declare @a date
select @a = "apr 12, 0001"
select datepart(hh, @a)
-----------
    0

--Find the month of a time
declare @a time
select @a = "20:43:22"
select datename(mm, @a)
------------------------------
January

When you give a null value to a datetime function as a parameter, NULL is returned.

Usage

datepart, a date function, returns an integer value for the specified part of a datetime value. For more information about date functions, see “Date functions”.
datepart returns a number that follows ISO standard 8601, which defines the first day of the week and the first week of the year. Depending on whether the datepart function includes a value for calweekofyear, calyearofweek, or caldayorweek, the date returned may be different for the same unit of time. For example, if Adaptive Server is configured to use U.S. English as the default language, the following returns 1988:
```
datepart(cyr, "1/1/1989")
```
However, the following returns 1989:
```
datepart(yy, "1/1/1989)
```
This disparity occurs because the ISO standard defines the first week of the year as the first week that includes a Thursday and begins with Monday.

For servers using U.S. English as their default language, the first day of the week is Sunday, and the first week of the year is the week that contains January 4th.
The date part weekday or dw returns the corresponding number when used with datepart. The numbers that correspond to the names of weekdays depend on the datefirst setting. Some language defaults (including us_english) produce Sunday=1, Monday=2, and so on; others produce Monday=1, Tuesday=2, and so on.You can change the default behavior on a per-session basis with set datefirst. See the datefirst option of the set command for more information.
calweekofyear, which can be abbreviated as cwk, returns the ordinal position of the week within the year. calyearofweek, which can be abbreviated as cyr, returns the year in which the week begins. caldayofweek, which can abbreviated as cdw, returns the ordinal position of the day within the week. You cannot use calweekofyear, calyearofweek, and caldayofweek as date parts for dateadd, datediff, and datename.
Since datetime and time are only accurate to 1/300th of a second, when these datatypes are used with datepart, milliseconds are rounded to the nearest 1/300th second.
Since smalldatetime is accurate only to the minute, when a smalldatetime value is used with datepart, seconds and milliseconds are always 0.
The values of the weekday date part are affected by the language setting.

Standards

ANSI SQL – Compliance level: Transact-SQL extension.

Permissions

Any user can execute datepart.