如何从PostgreSql中的预约返回工作时间？

create table reservation (during tsrange,EXCLUDE USING gist (during WITH &&)
 );

用于查找从给定日期和时间开始的时间表中的差距(2012-11-17 8：在下面的示例中)
它也发现了周六,周日和公众假期.
公共假期在表格中定义

create table pyha ( pyha date primary key)

如何排除周末和公众假期？

硬编码空闲时间作为保留查询之类的

with gaps as (
  select
    upper(during) as start,lead(lower(during),1,upper(during)) over (ORDER BY during) - upper(during) as gap
  from (
    select during
    from reservation
   union all values
     ('(,2012-11-17 8:)'::tsrange),-- given date and hour from which to find free work time
     ('[2012-11-17 0:,2012-11-18 24:)'::tsrange),-- exclude saturday
     ('[2012-11-18 0:,2012-11-19 8:)'::tsrange),-- exclude sunday
     ('[2012-11-19 18:,2012-11-20 8:)'::tsrange),('[2012-11-20 18:,2012-11-21 8:)'::tsrange),('[2012-11-21 18:,2012-11-22 8:)'::tsrange),('[2012-11-22 18:,2012-11-23 8:)'::tsrange),('[2012-11-23 18:,2012-11-24 24:)'::tsrange),('[2012-11-24 0:,2012-11-25 24:)'::tsrange),-- exclude saturday
     ('[2012-11-25 0:,2012-11-26 8:)'::tsrange)  -- exclude sunday
 ) as x
)
select *
  from gaps
where gap > '0'::interval
order by start

每个空闲时间范围都需要单独的联合行.

从给定的日期和时间开始,哪个是在工作日和工作时间(8：00~18：00)返回空闲时间的最佳方法？

更新

选择回答始终在8:00返回空闲时间.
如果在指定的开始日期之前不是在指定的开始时间之前返回空闲时间,例如,如果开始时间是9,则不是在2012-11-19 9:00之前返回？
开始时间可能只有值8,9,10,11,12,13,14,15,16或17

即使2012-11-19 8:00如果免费也应该返回2012-11-19 9:00.
只有在2012-11-19 9:00没有空闲时间,并且在接下来的工作日8:00首次免费时,它应该返回8:00.

我尝试通过将2012-11-19 9：添加到两个地方来解决这个问题,如下面的查询所示,但此查询仍然会在2012-11-19 8:00返回空闲时间.
如何解决这个问题,以便在2012-11-19 9:00返回空闲时间？

create table reservation (during tsrange,EXCLUDE USING gist (during WITH &&)
 );
create table pyha ( pyha date primary key);
with gaps as (
    select
        upper(during) as start,upper(during)) over (ORDER BY during) - upper(during) as gap
    from (
        select during
          from reservation
             where upper(during)>= '2012-11-19 9:'
       union all values
         ('(,2012-11-19 9:)'::tsrange)
        union all
        select
            unnest(case
                when pyha is not null then array[tsrange(d,d + interval '1 day')]
                when date_part('dow',d) in (0,6) then array[tsrange(d,d + interval '1 day')]
                else array[tsrange(d,d + interval '8 hours'),tsrange(d + interval '18 hours',d + interval '1 day')]
            end)
        from generate_series(
            '2012-11-19'::timestamp without time zone,'2012-11-19'::timestamp without time zone+ interval '3 month',interval '1 day'
        ) as s(d)
        left join pyha on pyha = d::date
    ) as x
)

select start,date_part('epoch',gap) / (60*60) as hours
  from gaps
where gap > '0'::interval
order by start

UPDATE2

我尝试了更新的答案,但它返回错误的数据.完整的测试用例是：

create temp table reservation  ( during tsrange ) on commit drop;
insert into reservation values(
'[2012-11-19 11:00:00,2012-11-19 11:30:00)'::tsrange );

with gaps as (
    select
        upper(during) as start,upper(during)) over (ORDER BY during) - upper(during) as gap
    from (
        select during
          from reservation
        union all
        select
            unnest(case
                when pyha is not null then array[tsrange(d,d + interval '1 day')]
                when d::date =  DATE'2012-11-19' then array[
                            tsrange(d,'2012-11-19 12:'),-- must return starting at 12:00
                            tsrange(d + interval '18 hours',d + interval '1 day')]
            end)
        from generate_series(
            DATE'2012-11-19'::timestamp without time zone,DATE'2012-11-19'::timestamp without time zone+ interval '3 month',interval '1 day'
        ) as s(d) 
        left join pyha on pyha = d::date
    ) as x 
)

select start,gap) / (60*60) as tunde
  from gaps 
where gap > '0'::interval
order by start

观察第一行：

"2012-11-19 11:30:00"

预期：

"2012-11-19 12:00:00"

怎么修 ？