How to clear stored substitution variables in Oracle SQL developer

Question

Suppose I have a query:

SELECT * from table1 tr where tr.start_time < &&starttime;

First time i execute the query, SQL Developer prompts me to enter the value for the substitution variable 'starttime' and is stored. Next time I run the script, it reuses the same value again, how do I reset/clear the stored value?

Answer 1

UNDEFINE starttime;

Just use above command.

Answer 2

Just use one ampersand at the start. You will be prompted to enter the value fresh. See the difference between & and &&