How to combine Countif & dropdown in the same cell.

[ArunKumarM]

Greeting of the day ,

I would like to combine Countif and dropdown in the same cell ,

Column1 would be Names of product
Column2 i would like to include a dropdown list of equipments that can be used for that product but same equipment cant be used on the same day for another product

I have been using this formula (=COUNTIF($B$4:$B$30,(B5:B31))=1) for avoiding duplication in the data validation
the problem is i am unable to create dropdown list .

any help is truly appreciated.

Thanks in advance
Arun