SELECT
  relatedCaseID,
  CaseRelationship.startDate,
  CaseHeader.caseReference
INTO
  :relatedCaseID,
  :startDate,
  :caseReference 
FROM
  CaseRelationship,
  CaseHeader 
WHERE CaseRelationship.caseID = :caseID 
  AND CaseRelationship.reasonCode = :reasonCode 
  AND CaseHeader.caseID = CaseRelationship.relatedCaseID