```ruby
class AddMissingUniqueIndexesForUniqueAttributes < ActiveRecord::Migration[5.0]
  def change
    tables = {
      country: [:name, :iso_name],
      option_type: [:name],
      option_value: [:name],
      promotion: [:path],
      refund_reason: [:name],
      reimbursement_type: [:name],
      return_authorization_reason: [:name],
      role: [:name],
      shipping_category: [:name],
      store: [:code],
      tax_category: [:name],
      tracker: [:analytics_id],
      zone: [:name]
    }

    tables.each do |table, columns|
      table_class = "Spree::#{table.to_s.classify}".constantize
      table_name = table_class.table_name

      columns.each do |column|
        unless index_exists?(table_name, column, unique: true)
          attributes = table_class.unscoped.group(column).having('sum(1) > 1').pluck(column)
          instances = table_class.where(column => [nil, attributes])

          instances.find_each do |instance|
            column_value = 'Unique String ' + SecureRandom.urlsafe_base64(8).upcase.delete('/+=_-')[0, 8]
            instance.send("#{column}=", column_value)
            instance.save
          end

          remove_index table_name, column if index_exists?(table_name, column)
          add_index table_name, "lower(#{column})", unique: true
        end
      end
    end
  end
end
```

Fix migrations on mysql database
user
```ruby
class AddMissingUniqueIndexesForUniqueAttributes < ActiveRecord::Migration[5.0]
  def change
    tables = {
      country: [:name, :iso_name],
      option_type: [:name],
      option_value: [:name],
      promotion: [:path],
      refund_reason: [:name],
      reimbursement_type: [:name],
      return_authorization_reason: [:name],
      role: [:name],
      shipping_category: [:name],
      store: [:code],
      tax_category: [:name],
      tracker: [:analytics_id],
      zone: [:name]
    }

    tables.each do |table, columns|
      table_class = "Spree::#{table.to_s.classify}".constantize
      table_name = table_class.table_name

      columns.each do |column|
        unless index_exists?(table_name, column, unique: true)
          attributes = table_class.unscoped.group(column).having('sum(1) > 1').pluck(column)
          instances = table_class.where(column => [nil, attributes])

          instances.find_each do |instance|
            column_value = 'Unique String ' + SecureRandom.urlsafe_base64(8).upcase.delete('/+=_-')[0, 8]
            instance.send("#{column}=", column_value)
            instance.save
          end

          remove_index table_name, column if index_exists?(table_name, column)
          if supports_expression_index?
            add_index table_name, "lower(#{column})", unique: true
          else
            add_index table_name, column, unique: true
          end
        end
      end
    end
  end
end
```
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