SQL statement Daquan (2) _ FUNCTION Daquan

---- Arithmetic functions ----

/*** Trigonometric function ***/
Sin (float_expression) -- returns the sine of the angle in radians
Cos (float_expression) -- returns the cosine of the angle in radians
Tan (float_expression) -- returns the tangent of the angle in radians
Cot (float_expression) -- returns the cotangent of the angle in radians
/*** Inverse trigonometric function ***/
Asin (float_expression) -- returns the angle in radians where the sine is the float value.
ACOs (float_expression) -- returns the angle in radians where the cosine is the float value.
Atan (float_expression) -- returns the angle in radians of the float value.
Atan2 (float_expression1, float_expression2)
-- Returns the radians of float_expression1/float_expres-sion2.
Degrees (numeric_expression)
-- Converts radians to degrees and returns data of the same type as the expressions.
-- Integer/money/real/Float Type
Radians (numeric_expression) -- converts degrees to radians and returns the same data type as the expression.
-- Integer/money/real/Float Type
Exp (float_expression) -- returns the exponent value of the expression.
Log (float_expression) -- returns the natural logarithm of the expression.
Log10 (float_expression) -- returns the base-10 logarithm of the expression.
SQRT (float_expression) -- returns the square root of the expression
/***** Approximate function ***/
Ceiling (numeric_expression) -- Return> = the minimum integer of the expression. The returned data type is the same as that of the expression.
-- Integer/money/real/Float Type
Floor (numeric_expression) -- returns the minimum integer of the <= expression. The returned data type is the same as that of the expression.
-- Integer/money/real/Float Type
Round (numeric_expression) -- returns the data returned from a rounding value with integer_expression as the precision.
-- The same type and expression can be integer/money/real/Float Type
ABS (numeric_expression) -- returns the absolute value of the expression. The returned data type is the same as that of the expression.
-- Integer/money/real/Float Type
Sign (numeric_expression) -- the positive and negative values of the test parameter return the data type returned by 0, zero, 1, positive, or-1 negative.
-- Same as the expression, it can be of the integer, money, real, or float type.
Pi () -- the return value is π, that is, 3.1415926535897936
Rand ([integer_expression]) -- use the optional [integer_expression] As the seed value to obtain a random floating point number between 0 and 1.

---- String function ----
ASCII () -- returns the ASCII value of the leftmost character of a character expression.
Char () -- function used to convert ASCII code to character
-- If no value is entered ~ The Char function returns a null value for the ASCII value between 255.
Lower () -- function converts all strings to lowercase letters
Upper () -- function converts all strings to uppercase
STR () -- function converts numeric data to numeric data
Ltrim () -- function removes spaces in the string Header
Rtrim () -- function removes spaces at the end of the string
Left (), right (), substring () -- The function returns some strings.
Charindex (), patindex () -- The function returns the starting position of a specified substring in the string.
Soundex () -- The function returns a four-digit escape code.
-- The soundex function can be used to find strings with similar sound. However, the soundex function returns only 0 values for numbers and Chinese characters.
Difference () -- the difference between the two character expressions returned by the soundex Function
-- 0 the first character returned by the two soundex functions is different
-- 1 the first character returned by the two soundex functions is the same
-- 2 two soundex functions return the same first and second characters.
-- 3 two soundex functions return the same first, second, and third characters.
-- 4 two soundex functions return identical values

Quotename () -- The function returns a string enclosed by a specific character.
/* Select quotename ('abc', '{') quotename ('abc ')
The running result is as follows:
----------------------------------{
{ABC} [ABC] */

Replicate () -- The function returns a string that repeats character_expression for a specified number of times.
/* Select replicate ('abc', 3) replicate ('abc',-2)
The running result is as follows:
----------------------
Abcabcabc null */

Reverse () -- The function reverses the character arrangement order of the specified string
Replace () -- returns the string with the specified substring replaced by the function.
/* Select Replace ('abc123g ', '123', 'def ')
The running result is as follows:
----------------------
Abcdefg */

Space () -- The function returns a blank string with a specified length.
Stuff () -- The function replaces a substring of the specified position length with another substring.

---- Data type conversion function ----
The syntax of the cast () function is as follows:
Cast () (<expression> as <data _ type> [length])
The convert () function syntax is as follows:
Convert () (<data _ type> [length], <expression> [, style])

Select cast (100 + 99 as char) convert (varchar (12), getdate ())
The running result is as follows:
------------------------------------------
199 Jan 15 2000

---- Date function ----
Day () -- The function returns the date value in date_expression.
Month () -- The function returns the month value in date_expression.
Year () -- returns the Year Value in date_expression.
Dateadd (<datepart>, <number>, <date>)
-- The function returns the new date generated by the specified date plus the specified additional date interval number.
Datediff (<datepart >,< number >,< date>)
-- The function returns the datepart differences between two specified dates.
Datename (<datepart>, <date>) -- The function returns the specified part of the date in the form of a string.
Datepart (<datepart >,< date>) -- The function returns the specified part of the date in the form of an integer.
Getdate () -- The function returns the current date and time of the system in the default format of datetime.

---- System functions ----
App_name () -- function returns the name of the currently executed application
Coalesce () -- function returns the value of the first non-null expression among multiple expressions.
Col_length (<'table _ name' >,< 'column _ name'>) -- returns the length value of the specified field in the table.
Col_name (<table_id >,< column_id>) -- the name of the specified field in the function return table is the column name.
Datalength () -- the actual length of the data returned by the function
Db_id (['database _ name']) -- number of the database returned by the function
Db_name (database_id) -- Name of the database returned by the function
Host_id () -- The function returns the name of the server computer.
Host_name () -- returns the name of the server computer.
Identity (<data_type> [, seed increment]) [as column_name])
-- The identity () function is used only in the select into statement to insert an identity column to the new table.
/* Select Identity (INT, 1, 1) as column_name
Into newtable
From oldtable */
Isdate () -- determines whether the given expression is a reasonable date.
Isnull (<check_expression >,< replacement_value>) -- The function replaces the null value in the expression with the specified value.
Isnumeric () -- The function determines whether the given expression is a reasonable value.
Newid () -- The function returns a value of the uniqueidentifier type.
Nullif (<expression1>, <expression2>)
-- The nullif function returns the value of expression1 if expression1 is equal to expression2. If the value is not equal, the return value is expression1.