PL / SQL in the SUBSTR () function usage (corresponding to the extracted character)

SUBSTR in two ways

Format 1: substr (string string, int a, int b); - string is a string, A is from the first few characters, B is the number of bits of the character

Format 2: substr (string string, int a); --string a string, A is started from the first number after taking several characters

Formats

SELECT SUBSTR('HARRY JING',1,4) VALUE
FROM DUAL

SELECT SUBSTR('HARRY JING',4) VALUE
FROM DUAL

Reference:
https://www.cnblogs.com/dshore123/p/7805050.html