This function returns a substring of the length length from the position position, out of the string string.
- If length is not specified, all of the characters to the end of the string are used.
- If position is negative, counting begins at the end of the string.
- If position is 0 or 1, the result begins from the first character of the string.
- MID is an alias for this function.
- For additional information, refer to REGEXP_SUBSTR.