Common date functions in SQL

Date used, that is, full spelling and abbreviations can all be expressed in parameters.
Year YY yyyy 1753   ~   9999  
Quarter qq q quarter 1   ~   4  
Month Mm m Month 1 ~   12  
Day   Of   Year Dy Y: the number of days in a year. 1 - 366  
Day Dd d, 1 - 31  
Weekday dw w day of the week, the day of the week 1 - 7  
Week wk WW week, week of the year 0   ~   51  
Hour hh h 0 ~   23  
Minute MI n minutes 0 ~   59  
Second SS s seconds 0   ~   59  
Millisecond MS - Millisecond 0   ~   999  
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1 : Getdate () Function
Returns the current time.
Select   Getdate ()

-- ----------------------------------------------------
2009 - 02 - 05   11 : 18 : 39.770

(The number of affected rows is1Rows)

========================================================== ============================
2 : Dateadd Function
The first parameter is the type to be added, such as mm, the second parameter, and the third parameter is where you want to add
Select   Dateadd (M, 2 , ' 2004-1-1 ' ) [ Datelihan ]
Datelihan
-- ----------------------------------------------------
2004 - 03 - 01   00 : 00 : 00.000

(The number of affected rows is1Rows)

Select   Dateadd (Yy, 1 , ' 2004-1-1 ' ) [ Datelihan ]
Datelihan
-- ----------------------------------------------------
2005 - 01 - 01   00 : 00 : 00.000

(The number of affected rows is 1 Rows)
========================================================== ========================================================== ===
3 : Datediff Function
Returns the difference value between two dates, parameter 2 and parameter 3. - Parameter 2 return type: parameter 1
Select   Datediff (DD, ' 2009-12-27 ' , ' 9-12-25 ' ) [ Datelihan ]
Datelihan
-- ---------
- 2

(The number of affected rows is 1 Rows)
Select   Datediff (Yy, ' 2007-12-27 ' , ' 9-12-25 ' ) [ Datelihan ]
Datelihan
-- ---------
2

(The number of affected rows is 1 Rows)
========================================================== ========================================================== =
4 : Datepart Function
Returns the value of parameter 1 corresponding to parameter 2.
Select   Datepart (Mm, ' 2008-08-07 ' ) [ Month ]
Select   Datepart (Yy, ' 2008-08-07 ' ) [ Year ]
Month
-- ---------
8

(The number of affected rows is1Rows)

Year
-----------
2008

(The number of affected rows is1Rows)

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5 : Datename Function
Returns a string representing the specified date part of a specified date.
Select   Datename (Weekday, ' ' ) [ Week ]
Week
-- ----------------------------
Thursday

(The number of affected rows is1Rows)

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6 : the day function
returns an integer indicating the date specified by the parameter, which is the day of the month
select day ( ' 2009-2-5 ' ) [ day ]
day
-- ---------
5

(the number of affected rows is 1 line)
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7 : the month function
returns an integer indicating the date of the Year of the specified parameter
select month ( ' 2007-04-30 ' );
-- ---------
4

(the number of affected rows is 1 line)
=================================================== ========================================================== ===

8: Year Function
Returns an integer indicating the year of the date specified by the parameter.
Select Year('2007-04-30');
-----------
2007

(The number of affected rows is 1 Rows)
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For example, you want to query records less than 10 days ago.
Select   *   From Tablename Where   Datediff ( Day , Your Date field, Getdate ()) < 10
For example, you want to query records within a period of time.
Select   *   From Talbename Where Your Date Field Between Date 1 And Date 2