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