Problem

You would like to use a legacy or a database you don’t have control over, with Phoenix, but the primary key of the table it is not named ‘id’.

** (Mariaex.Error) (1054): Unknown column 'p0.id' in 'field list'

Solution

You can define the primary key using the @primary_key as in:

 @primary_key {:id_other_name, :integer, []}
  schema "db_table" do
    field :description, :string
    ...
  end

Taken from here