Oracle system functions

1.single-row Functions

NVL
NVL2
Nullif
Coalesce
Case
DECODE

2.Character functions

LOWER (column|expression)--lowercase
UPPER (column|expression)--uppercase
Initcap (column|expression)--Capitalize first letter
CONCAT (Column1|expression1,column2|expression2)--string connection, equivalent to | |
SUBSTR (Column|expression,m[,n])--take substring, M: first n: How many digits to take
Length (column|expression)--Returns the length of the string
INSTR (column|expression, ' string ', [, M], [n])--Returns the position of the specified string in the query string, m: first N: Number of
Lpad (column|expression, N, ' string ')--left-padded, n-length, not enough to fill string
Rpad (column|expression, N, ' string ')--right-padded, n-length, not enough to fill string
TRIM (Leading|trailing|both trim_character from Trim_source)--Go
Replace (text,search_string,replacement_string)-Alternative

3.Number Functions

ROUND (Column|expression, N): (rounded) Rounds value to a specified decimal
TRUNC (Column|expression, N): (direct truncation) truncates value to a specified decimal
MOD (m,n): (redundancy) Returns remainder of division

4.Date functions

Months_between (' 01-sep-95 ', ' 11-jan-94 ')--calculates how many months of two days
Add_months (' 31-jan-96 ', 1)--How many months after a certain date
Next_day (' 01-sep-95 ', ' FRIDAY ')--the date of the next Friday
Last_day (' 01-feb-95 ')--the last day of one months
ROUND (sysdate, ' month ')--truncated from month (rounded)
TRUNC (sysdate, ' month ')--truncated from month (direct truncation)

Oracle system functions