Duplicate entries based on one question

I'm trying to gather information about how many courses are available for a specific industry. But i don't want to end up with 5000 entries all the same.

Can it be that every entry is checked against what has already been submitted and then reject the entry if it is already in another submission 

I've seen answers as it refers to duplicate emails or phone numbers but I can't see that would work for this. 

Any suggestions please. ?

Yes, this is possible by setting a Unique Question.

Set the field that you don't want duplicates as Unique Question in your form settings.

Help Article: How to set Form Limits Based on a Unique Question

Let us know if you have further questions.