text: CREATE TABLE drug_era
  (
    drug_era_id					INTEGER			NOT NULL ,
    person_id						INTEGER			NOT NULL ,
    drug_concept_id				INTEGER			NOT NULL ,
    drug_era_start_date			DATE			NOT NULL ,
    drug_era_end_date				DATE			NOT NULL ,
    drug_exposure_count			INTEGER			NULL ,
    gap_days						INTEGER			NULL
  )
  ;