尝试：

CREATE OR REPLACE VIEW my_view AS
WITH date_bookends AS (
  SELECT LEAST(MIN(t.sampled_on), MIN(t.received_on), MIN(t.completed_on), MIN(t.authorized_on)) 'min_date'
         GREATEST(MAX(t.sampled_on), MAX(t.received_on), MAX(t.completed_on), MAX(t.authorized_on)) 'max_date'
    FROM SAMPLE t),
    all_hours AS (
  SELECT t.min_date + numtodsinterval(LEVEL - 1,'hour') date_by_hour
    FROM date_bookends t
CONNECT BY LEVEL <= ( t.max_date - t.min_date + 1) * 24)
SELECT h.date_by_hour,
       COUNT(CASE WHEN h.hour = TRUNC(s.sampled_on,'hh24') THEN 1 END) sampled#
       COUNT(CASE WHEN h.hour = TRUNC(s.received_on,'hh24') THEN 1 END) received#
       COUNT(CASE WHEN h.hour = TRUNC(s.completed_on,'hh24') THEN 1 END) completed#
       COUNT(CASE WHEN h.hour = TRUNC(s.authorized_on,'hh24') THEN 1 END) authorized#
  FROM all_hours h
CROSS JOIN sample s
  GROUP BY h.hour

不使用子查询分解：

CREATE OR REPLACE VIEW my_view AS
SELECT h.date_by_hour,
       COUNT(CASE WHEN h.hour = TRUNC(s.sampled_on,'hh24') THEN 1 END) sampled#
       COUNT(CASE WHEN h.hour = TRUNC(s.received_on,'hh24') THEN 1 END) received#
       COUNT(CASE WHEN h.hour = TRUNC(s.completed_on,'hh24') THEN 1 END) completed#
       COUNT(CASE WHEN h.hour = TRUNC(s.authorized_on,'hh24') THEN 1 END) authorized#
  FROM (SELECT t.min_date + numtodsinterval(LEVEL - 1,'hour') date_by_hour
         FROM (SELECT LEAST(MIN(t.sampled_on), MIN(t.received_on), MIN(t.completed_on), MIN(t.authorized_on)) 'min_date'
                            GREATEST(MAX(t.sampled_on), MAX(t.received_on), MAX(t.completed_on), MAX(t.authorized_on)) 'max_date'
                       FROM SAMPLE t) t
CONNECT BY LEVEL <= ( t.max_date - t.min_date + 1) * 24) h
CROSS JOIN sample s
GROUP BY h.hour

该查询两次访问SAMPLES表-第一次获取最早和最新的日期来构造date_by_hour值的构造。