Example of using the datediff function in Sqlserver

The DATEDIFF () function returns the number of days between two dates.

Syntax

DATEDIFF (datepart, startdate, enddate)

The startdate AND enddate parameters are valid date expressions.

You need to know how many days the difference between a specified date and February 1, January 1. Therefore, you can use datediff to obtain:

The code is as follows:	Copy code
Print datediff (day, '1-1-1-1 ', '2017-05-25 ')

The execution result is 4892, which is obviously an error value. Which day Does 1-1 correspond? Use dateadd to calculate:

The code is as follows:	Copy code
Print dateadd (day,-4892, '2017-05-25 ')

The execution result is January 1. That is to say, the script cannot be expressed as 1-1-1 on January 1:

The code is as follows:	Copy code
Print datediff (day, '2017-1-1 ', '2017-05-25 ')

The error message is as follows:

Reference content

Message 242, level 16, Status 3, 1st rows
Conversion from the varchar data type to the datetime data type generates a value out of the range.

0001-1-1 cannot be converted to datetime? For more information, see the SQL Server Documentation. The date range of the datetime type is January 1, January 1-9, 1753, December 31, 999. The datediff parameter is also subject to this restriction.

Why is the minimum datetime time January 1, 1753? Baidu:

Reference content

In the past, there were two calendars in the West: the ellipsis and the Gregorian calendar, which were different for a few days. When you use the ellipsis to transfer to the Gregorian calendar, you need to skip 10-13 days. Therefore, to store dates earlier than 1753, you must know which calendar is used and process the skipped 10 to 13 days. Most Western countries converted calendars in 1753.

Attached datdiff function parameters

Datepart	Abbreviations
Year	Yy, yyyy
Quarter	Qq, q
Month	Mm, m
Day of the year	Dy, y
Day	Dd, d
Week	Wk, ww
Week	Dw, w
Hours	Hh
Minutes	Mi, n
Seconds	Ss, s
Millisecond	MS
Subtle	Mcs
Nanoseconds	Ns