One, the string function
1, ASCII (' string ')--Returns the ASCII code value of the leftmost character of the string
Select ASCII (' a ')--Returns 97
Select ASCII (' ABCD ')--also returns 97
2, CHAR (' Integer ')--converts ASCII value to character, integer range 0-255
Select CHAR (' 97 ')--return a
3, LEN ()--Returns the length of the given string, without trailing spaces
Select LEN (' AASSDD ')--return 6
Select LEN (' AASSDD ')--return 8
Select LEN (' AASSDD ')--return 8
4. Left--intercept string
Left (' string ', number of digits)
Select Left (' ABCDEFG ', 3)--Return to ABC
Right--intercept string
Select Right (' ABCDEFG ', 3)--back to EFG
5, Lower and upper
Select LOWER (' AbCdEfG ')--return to AbCdEfG
Select UPPER (' AbCdEfG ')--return to AbCdEfG
Second, date and time functions
1, DATEADD--add a period of time to the specified date to return a new datetime value
DATEADD (time interval type (year, month, day), Interval time (integer), ' Time Date ')
Example: Select DATEADD (month,2, ' 1993-08-28 ')--return to 1993-10-28
2, DATEDIFF--Find the difference between two dates
Format: DATEDIFF (time interval type (year, month, day), ' Start time ', ' End Time ')
Select DATEDIFF (year, ' 1990-03-02 ', ' 1997-12-08 ')--return 7
Select DATEDIFF (MONTH, ' 1990-03-02 ', ' 1997-12-08 ')--return 93
Select DATEDIFF (Day, ' 1990-03-02 ', ' 1997-12-08 ')--return 2838
3, day, month, year--the date of the month of removal
Format: Day (data), MONTH (data), year (data)
Select Day (' 1987-09-18 ')--return 18
Select MONTH (' 1987-09-18 ')--return 9
Select year (' 1987-09-18 ')--return 1987
4, GETDATE--Take the current system time
Select GETDATE ()--return current time 2015-04-01 11:01:30.687
Third, numerical functions
1. CEILING Ceiling Number (returns the smallest integer greater than or equal to the given number)
Floor number (returns the largest integer less than or equal to the given number)
Select CEILING (5.4)--Return 6
Select Floor (5.4)--Return 5
2. RAND
Select RAND ()--generates a random float number between 0-1
3. POWER--return
Select POWER (3,2)--Return 9
Select POWER (2.15,3)--Return 9.94
4. Convert-type conversion (cast ... As is also a type conversion)
Example: birthday=1997-8-28
CAST (Year (BIRTHDAY) as varchar (10) + ' Years ' +mouth (BIRTHDAY) as varchar (10) + ' month ' +day (BIRTHDAY) as varchar (10) + ' Day ')
Date changed after execution: August 28, 1997
April 1 SQL Common functions