When you are inserting data into Oracle tables in SQL*Plus using hard-coded string, some of the character fields may contain the ampersand character (&). The following is an example:
insert into dept (deptno, deptname) values(20,'R&D');
However, within SQL*Plus, "&" is treated as a substitution character by default. Thus, the above statement will prompt you to enter an input value for D. To turn off this behavior, you can alter your substitution character by using the SET command available in SQL*Plus:
SQL> SET DEFINE ~
The DEFINE parameter defines the substitution control character and sets it to "~" in the above statement. Now you can insert strings with "&" characters in them and reset the substitution character back to "&" when you need to.