Use the SUBSTRING() function to extract part of a string. The SUBSTRING() function’s important characteristics are:
A substring is any sequence of contiguous characters from the source string, including an empty string or the entire source string itself.
SUBSTRING() extracts part of a string starting at a specified position and continuing for a specified number of characters.
A substring of an empty string is an empty string.
If any argument is null, SUBSTRING() returns null. (But see the Oracle exception in the DBMS Tip in this section.)
SUBSTRING(string FROM start [FOR length])