query add prefix when duplicate record in item number column

[Arnold]

Hello All
I need to add a query for a column that will duplicate the ItemNumber Column but identify if there are duplicate values in that column and if so it will add a prefix 1- for the first duplicate and 2- for the next an so on, and do the same for each set of duplicates.
Ex. ItemNumber
5698326
1-5698326
2-5698326
698325


1-698325
2-698325


Thanks in advance for the help

[orange]

Please tell readers the rationale for this. What is the issue that is solved by this approach?

[Arnold]

We create sku numbers based on the item number. Therefore we sometimes need to have the item in the system listed twice (when there are 2 ASINs for one item in amazon lets say).

[orange]

2 ASINs???
I think you are saying you need a unique identifier within some context, but it's a guess.