Usage of substr in "base" Oracle

simple usage of substr functions in Oracle

SUBSTR (string, intercept start position, intercept length)//return intercepted word

substr (' Hello World ', 0, 1)//return result is ' H ' * start with a string of length 1 from the first character

substr (' Hello World ', 1, 1)//Returns the result for ' H ' *0 and 1 is the first character that represents the start position of the Intercept

substr (' Hello world ', 2,4)//return result as ' Ello '

substr (' Hello world ', -3,3)//Returns the result as ' rld ' * negative (-i) to indicate the start of the intercept is the left number I character of the right end of the string

Test:

Select substr (' Hello world ', -3,3) value from dual;

Usage of substr in "base" Oracle