Oracle SQL self-function collation

numeric functions
ABS (N): Used to return the absolute value of the number n
Ceil (N): Returns the smallest integer greater than or equal to the number n
Floor (N): Returns the largest integer less than or equal to the number n
MoD (M,n): Returns the remainder after dividing the m/n number, or if n=0, returns m
Round (N,[m]): Performs a rounding operation, rounding to the integer digits if omitted m.
If M is a negative number, it is rounded to the M-bit before the decimal point. Rounded to M-bit after decimal if M is positive
Sign (n): This function is used to detect the positive or negative of the number N. If the number n is less than 0 returns-1.
Returns 0 if the number n equals zero. Returns 1 if the number n is greater than 0.
Trunc (N,[m]): This function is used to intercept numbers. If the number M is omitted, the decimal part of the number n is truncated.
If the number m is positive, the number n is truncated to the first m bit after the decimal point.
If the number m is negative, the number n is truncated to the M-bit before the decimal point.

Character functions
Ascⅱ (char): This function is used to return the Ascⅱ code value of the first character of a string
Chr (n): This function is used to convert Ascⅱ code values into characters
Concat (CHAR1,CHAR2): For connection string, action and connection operator ' | | ' Exactly the same
Lower (char): Converts all uppercase letters to lowercase letters
Uppper (char): Convert all lowercase letters to uppercase
Initcap (char): Converts the first letter of each word in a string to uppercase
Trim (char from string): used to truncate specific characters from the head/tail or both ends of a string.
The argument char is the character to truncate, and string is the source.
LTrim (Char1[,set]): This function is used to remove any character in a set contained in a string char1 the left.
Oracle starts scanning from the first character on the left, removing the characters that appear in the set one at a-
Terminates when a character not in set is encountered, and then returns the remaining result.
RTrim (Char1[,set]): This function is used to remove any character in the set contained in the right end of the string char1.
Oracle starts scanning from the first character on the right, removing the characters that appear in the set,
Terminates when a character not in set is encountered, and then returns the remaining result.
Lpad (CHAR1,CHAR2): This function is used to populate the left end of a string with a string char2.
The default value until the total length of the string is N,char2 is a space.
If the char1 length is greater than N, the function returns n characters from the left end of the char1.
Rpad (): This function is used to populate string char2 at the right end of the string.
The default value until the total length of the string is N,char2 is a space.
If the char1 length is greater than N, the function returns n characters from the left end of the char1.
Length (char): Used to return string lengths, or null if char is NULL
InStr (): Used to get the position of the substring in the string. Where the number n is the starting search location,
The number M is the number of substring occurrences. If the number n is negative, the search starts at the tail.
The number m must be a positive integer, and the default value of N and M is 1.
SUBSTR (Char,m[,n]): This function is used to get the substring of a string, where the number m is the beginning of the string.
The number n is the length of the substring. If M is 0, start with the first character. If M is negative, it starts at the tail.
Least (Expr_list): Returns the smallest of the values in the expression list. If the expression type is different, it is implicitly converted to the first expression type.
Greatest (Expr_list): Returns the largest of the values in the expression list. If the expression type is different, it is implicitly converted to the first expression type.

Date function
Add_months (d,n): Used to return datetime
Last_day (d): Used to return the last day of the month in which a particular date is located
Extract: Used to get the specific data you need from a datetime value. Extract (year from sysdate)
Current_date|sysdate: The datetime that is used to return the current session time zone
Next_day (D,char): Used to return the first working day after a specified date ( Date
Round (d[,fmt]): The rounding result used to return the DateTime, as specified by Char.
If the year is specified, July 1 is the dividing line.
If the month is specified, 16th is the dividing line.
If the day is specified, it is the dividing line at 12:00 noon.
Trunc (d[,fmt]): Used to truncate date-time data.
If FMT specifies the year, the result is January 1 of the current year.
If FMT specifies the month, the result is 1st this month.