Syntax:
SUBSTRING(str,pos), SUBSTRING(str FROM pos), SUBSTRING(str,pos,len),
SUBSTRING(str FROM pos FOR len)

The forms without a len argument return a substring from string str
starting at position pos. The forms with a len argument return a
substring len characters long from string str, starting at position
pos. The forms that use FROM are standard SQL syntax. It is also
possible to use a negative value for pos. In this case, the beginning
of the substring is pos characters from the end of the string, rather
than the beginning. A negative value may be used for pos in any of the
forms of this function. A value of 0 for pos returns an empty string.

For all forms of SUBSTRING(), the position of the first character in
the string from which the substring is to be extracted is reckoned as
1.

URL: https://dev.mysql.com/doc/refman/8.0/en/string-functions.html

