How to check id of one table into another table using php variable?

I have two tables named

product(id,pname,price) 

and

add_to_card(id,pid,is_added)

The problem is that I want to check the product_id which is either exist or not on add_to_card table.

This is my controller:

public function add_to_card(){

   $pid = request('pid'); //I want to check this $pid on add_to_card table

}

I have no idea how to resolve this.. Please help me?

via Chebli Mohamed