Count Number of double entries

I think you should probably follow Mark's advice of using two tables - especially as you indicate you are new to the product. But I just want to point out that using script you can easily implement exactly what you want without any additional tables or relationships. Moreover, a script solution will not hit arbitrary limitations as your description of the problem is refined or additional requirements come into view. For example, although you literally asked for a "count" - and that is what I implemented - but you might actually want a summary of the information and perhaps a drill down link to explore related records. All of this would be possible with script in just a few lines of code.

But again I just want to point out the superiority of using script!

Here is my quick demo (it took me only 5 minutes to put together):

View any record and [Count] will display the total number of records with the same [Name].

Count Similar Records ~ List All
https://haversineconsulting.quickbase.com/db/bncw958tt?a=td

Pastie Database
https://haversineconsulting.quickbase.com/db/bgcwm2m4g?a=dr&rid=618