how can I rewrite the query in more effecient way say using the with clause:

SELECT DISTINCT
       work_number,
       FIRST_VALUE (comments)
          OVER (PARTITION BY work_number ORDER BY comments_date DESC)
          AS comments,
       FIRST_VALUE (comments_date)
          OVER (PARTITION BY work_number ORDER BY comments_date DESC)
          AS comments_date,
       FIRST_VALUE (comments_source)
          OVER (PARTITION BY work_number ORDER BY comments_date DESC)
          AS comments_source,
       FIRST_VALUE (comment_type)
          OVER (PARTITION BY work_number ORDER BY comments_date DESC)
          AS comments_type
FROM (SELECT c.work_number,
             CASE
                WHEN c.comments IS NULL THEN 'no comment entered'
                ELSE c.comments
             END
                AS comments,
             c.comments_date,
             'n/a' comments_source,
             'General' comment_type
      FROM myschema.ledg_work_comment c
      UNION
      SELECT ls.work_number,
             CASE
                WHEN s.comments IS NULL THEN 'no comment entered'
                ELSE s.comments
             END
                AS comments,
             ls.status_date comments_date,
             'n/a' comments_source,
             'Status' comment_type
      FROM myschema.v_ledg_work_last_status ls, myschema.ledg_work_status s
      WHERE ls.work_status_id = s.work_status_id
      UNION
      SELECT r.work_number,
             CASE
                WHEN r.comments IS NULL THEN 'no comment entered'
                ELSE r.comments
             END
                AS comments,
             r.receipt_adj_date comments_date,
             'n/a' comments_source,
             CASE
                WHEN r.receipt_adj_type = 'R' THEN 'Receipt'
                ELSE 'Adjustment'
             END
                AS comment_type
      FROM myschema.ledg_work_receipt r);