edit migration file

db/migrate/20191202023059_add_company_code_to_company.rb

@@ -2,4 +2,5 @@ class AddCompanyCodeToCompany < ActiveRecord::Migration[6.0]
   def change
   def change
     add_column :companies, :company_code, :string, unique: true
     add_column :companies, :company_code, :string, unique: true
   end
   end
+  add_index :companies, :company_code, unique: true
 end
 end

db/migrate/20191202023440_add_index_to_company_code.rb

-class AddIndexToCompanyCode < ActiveRecord::Migration[6.0]
-  def change
-    add_index :companies, :company_code, unique: true
-  end
-end