returns the substring of string that begins at the nth character and is of length length, padded with pad if necessary. The n must be a positive whole number. If n is greater than LENGTH(string), then only pad characters are returned.
If you omit length, the rest of the string is returned. The default pad character is a blank.
SUBSTR('abc',2) -> 'bc'
SUBSTR('abc',2,4) -> 'bc '
SUBSTR('abc',2,6,'.') -> 'bc....'