即使添加了别名，我也收到了一个错误....为什么？

Question

SELECT * FROM 

(select 
flight_id,
flight_no,
scheduled_departure,
scheduled_arrival,
cast (scheduled_departure as text) TIMINGS
from bookings.flights), as TABLE1

case when TIMINGS
between 02:00:00+05:30 to 06:00:00+05:30 then 'Early morning flights'
when scheduled_departure to scheduled_arrival 

between 06:00:00+05:30  to 11:00:00+05:30 then 'Morning flights'
when scheduled_departure to scheduled_arrival 

between 11:00:00+05:30 to 16:00:00+05:30 then 'Noon flights'
when scheduled_departure to scheduled_arrival 

between 16:00:00+05:30 to 19:00:00+05:30 then 'Evening flights'
when scheduled_departure to scheduled_arrival 

between 19:00:00+05:30 to 23:00:00+05:30 then 'Night flights'
when scheduled_departure to scheduled_arrival 

between 23:00:00+05:30 to 02:00:00+05;30  then 'Night flights'
END as TIMINGS

这是错误

ERROR:  subquery in FROM must have an alias
LINE 1: SELECT * FROM (select 
                      ^
HINT:  For example, FROM (SELECT ...) [AS] foo.
SQL state: 42601
Character: 15

Answer 1

您完全无需CASE 即可获得所需的内容。
要意识到的一件事是，当使用日期/时间戳转换为文本时几乎总是不必要和不正确的（就像这里的情况一样）基本上只是不这样做。使用Postgres date functions。

以下给出了您想要的。它开始创建一个 CTE 来定义时间段和每个时间段的描述性名称。然后它将该 CTE 与飞行表连接起来。 （见演示here）

with departures( stime, etime, description)  as 
     (values ('00:00:00'::time, '02:00:00'::time, 'Night flight') 
           , ('02:00:00'::time, '06:00:00'::time, 'Early morning flight')
           , ('06:00:00'::time, '11:00:00'::time, 'Morning flight')
           , ('11:00:00'::time, '16:00:00'::time, 'Noon flight')
           , ('16:00:00'::time, '19:00:00'::time, 'Evening flight')
           , ('19:00:00'::time, '24:00:00'::time, 'Night flight')
     )
select f.flight_id                                        "Flight Id" 
     , (f.departure at time zone 'Asia/Kolkata')::time(0) "Schedule Departure Time" 
     , d.description                                      "Description" 
   from departures d
   join flights    f 
     on (   (f.departure at time zone 'Asia/Kolkata')::time(0) >= d.stime 
        and (f.departure at time zone 'Asia/Kolkata')::time(0) <  d.etime 
        )
 order by  "Schedule Departure Time";

注意事项：

• 时间戳始终包含日期和小数秒。自从你 想要只是时间比较都需要被丢弃。这是 使用::time(0) 完成。但是，它确实会四舍五入到最接近的 第二。
• 我更改了您对“夜间飞行”的定义。在时间戳中，之后 丢弃日期得到的时间，23:00:00 将总是 大于02:00:00。更改纠正了这一点。
• 我使用 “亚洲/加尔各答”时区来获得 +3.5 小时 从 UTC 偏移（在 UTC-5 时）。取决于您的服务器时区 设置你可能不需要这个。

我是新手，如果格式不规范，请多多包涵。 所以我在写完这段代码后得到了预期的输出......

'''
with flights ( stime, etime, description)  as 
     (values ('00:00:00'::time, '02:00:00'::time, 'Night flight') 
           , ('02:00:00'::time, '06:00:00'::time, 'Early morning flight')
           , ('06:00:00'::time, '11:00:00'::time, 'Morning flight')
           , ('11:00:00'::time, '16:00:00'::time, 'Noon flight')
           , ('16:00:00'::time, '19:00:00'::time, 'Evening flight')
           , ('19:00:00'::time, '24:00:00'::time, 'Night flight')
      )
      select flight_id               "Filght ID"
      ,     flight_no                "Flight No"
      ,     scheduled_departure      "scheduled_departure"
      ,     scheduled_arrival        "scheduled_arrival"
      ,     flights                  "Timings"
      from flights  
      join bookings.flights    f 
     on (   (scheduled_departure at time zone 'Asia/Kolkata')::time(0) >= stime 
        and (scheduled_arrival at time zone 'Asia/Kolkata')::time(0) <  time 
        )

''' 但在修改后的列中，我只想要诸如“夜间飞行”之类的文本，而不是“00:00:00”::time、“02:00:00”::time、“夜间飞行”的整个时间 我怎样才能得到文本输出？

第二次我尝试使用havin'或where语句过滤输出 使用此代码

 with flights ( stime, etime, description)  as 
     (values ('00:00:00'::time, '02:00:00'::time, 'Night flight') 
           , ('02:00:00'::time, '06:00:00'::time, 'Early morning flight')
           , ('06:00:00'::time, '11:00:00'::time, 'Morning flight')
           , ('11:00:00'::time, '16:00:00'::time, 'Noon flight')
           , ('16:00:00'::time, '19:00:00'::time, 'Evening flight')
           , ('19:00:00'::time, '24:00:00'::time, 'Night flight')
      )
      select flight_id               "Filght ID"
      ,     flight_no                "Flight No"
      ,     scheduled_departure      "scheduled_departure"
      ,     scheduled_arrival        "scheduled_arrival"
      ,     flights                  "Timings"
      from flights  
      join bookings.flights    f 
     on (   (scheduled_departure at time zone 'Asia/Kolkata')::time(0) >= stime 
        and (scheduled_arrival at time zone 'Asia/Kolkata')::time(0) <  etime 
        )
        group by 
        flight_id,
        flights 
having flights = 'Morning flight'

这样说给我一个错误

错误：未实现匿名复合类型的输入 第 22 行：有航班 = '早上的航班'

（粘贴文本，因为我的帐户中允许使用图片）

@belayer