SELECT number_of_hospitlizations, 
       count(*) AS persons_freq
FROM (
  SELECT person_id, COUNT(*) AS number_of_hospitlizations
  FROM (
      SELECT distinct condition_era_id, era.person_id  
      FROM (
          SELECT condition_start_date, condition_end_date, person_id
          FROM (SELECT visit_occurrence_id, condition_start_date, condition_end_date, person_id 
                FROM   condition_occurrence 
                WHERE  condition_concept_id=31967
                AND    visit_occurrence_id IS NOT NULL) AS FROM_cond
          JOIN (SELECT visit_occurrence_id, place_of_service_concept_id 
                FROM   visit_occurrence 
                WHERE  place_of_service_concept_id=9201) AS FROM_visit
          ON FROM_cond.visit_occurrence_id=FROM_visit.visit_occurrence_id
         ) AS occurr,
         (
          SELECT condition_era_id, person_id, condition_era_start_date, condition_era_end_date
          FROM   condition_era
          WHERE  condition_concept_id=31967
         ) AS era
      WHERE era.person_id=occurr.person_id 
        AND era.condition_era_start_date <= occurr.condition_end_date 
        AND (era.condition_era_end_date IS NULL OR era.condition_era_end_date >= occurr.condition_start_date)
     )
  GROUP BY person_id
  ORDER BY number_of_hospitlizations desc
  )
GROUP BY number_of_hospitlizations
ORDER BY persons_freq desc