Mysql2::Error: Table 'table_name' doesn't exist: SHOW FULL FIELDS FROM `table_name`

It is likely caused by ActiveRecord::Migration[5.1]. When you want to add foreign key to companies table, Migration read the tables first, but it doesn't exist.

Changing Migration to 5.0 works for me.

class CreateCompanies < ActiveRecord::Migration[5.0]
end

Or remove foreign options at first, and manually add foreign key later :

class CreateCompanies < ActiveRecord::Migration[5.1]
  def change
    create_table :companies do |t|
      t.string :ragione_sociale
      t.references :forma_giuridica # without :foreign_key option
      # ...
    end

    # add foreign key here
    add_reference :companies, :forma_giuridica
  end
end

::Migration[5.0] uses primary key int(11)

and

::Migration[5.1] uses primary key bigint(20)

The most common reasons are that when creating a foreign key, both the referenced field and the foreign key field need to match:

• Engine should be the same e.g. InnoDB
• Datatype should be the same, and with same length.
  e.g. VARCHAR(20) or INT(10) UNSIGNED
• Collation should be the same. e.g. utf8
• Unique - Foreign key should refer to field that is unique (usually private) in the reference table.