How can I avoid double entry?

Please, how do one avoid multiply entry of the same data?

This is essential in order not to flood the data base with the same data.

Thank you for contacting us.

You can use our unique submission feature to block multiple submissions from one system of one IP address by setting the "Loose check" or "Strict Check" respectively. Inside of this article you can see how to set Unique Submissions on a Form:  http://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form 

You can also use our unique question feature to prevent from submitting duplicate submissions. Example: You can set one of your forms question (like cell number or email address) to be a unique question. This will not allow a user to use the same cell number or email address to submit your form. Here is a guide to help you:  http://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

Hope this will help. Let us know if you need further assistance.