Consulta Oracle SQL para agrupar registros consecutivos

SELECT line_no,
       amount,
       narration,
       SUM( x ) OVER ( ORDER BY line_no
                       ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW 
       ) as calc_group
FROM (
  SELECT t.*,
         CASE lag( narration ) OVER (order by line_no ) 
         WHEN narration THEN 0
         ELSE 1 END x
  FROM test t

)
ORDER BY line_no