```ruby
class CreateIndices < ActiveRecord::Migration

  def change

    add_index :studies, :nct_id
    add_index :reported_events, :nct_id
    add_index :reported_events, :event_type
    add_index :reported_events, :subjects_affected
    add_index :facilities, :nct_id
    add_index :outcomes, :nct_id
    add_index :outcome_measured_values, :title

  end

end
```

Add indexes to the StudyXmlRecords table
user
```ruby
class CreateIndices < ActiveRecord::Migration

  def change

    add_index :studies, :nct_id
    add_index :reported_events, :nct_id
    add_index :reported_events, :event_type
    add_index :reported_events, :subjects_affected
    add_index :facilities, :nct_id
    add_index :outcomes, :nct_id
    add_index :outcome_measured_values, :title
    add_index :study_xml_records, :nct_id
    add_index :study_xml_records, :created_study_at

  end

end
```
assistant