Halting a script if it has already been run
How do I stop a script if it has already been run? I have several tables with different pieces of information that all relate back to one study (e.g. changes made, people added, etc.) and I have a running list of everything that happens to each study in another table called "history". But if by accident I click the button twice to run the script that creates an entry into the history table indicating that something has been done to this study, I get duplicate records. I want the script to halt if it has already been run.
thanks so much for all your help.