Postgresql 在“选择”中显示每个位置的本地时区_Postgresql_Timestamp With Timezone

Postgresql 在“选择”中显示每个位置的本地时区

postgresql

Postgresql 在“选择”中显示每个位置的本地时区,postgresql,timestamp-with-timezone,Postgresql,Timestamp With Timezone,我有一个火车乘车表，使用以下示例代码： CREATE TABLE train_rides ( trip_id bigserial PRIMARY KEY, origination text NOT NULL, destination text NOT NULL, departure timestamp with time zone NOT NULL, arrival timestamp with time zone NOT NULL ); INSERT

我有一个火车乘车表，使用以下示例代码：

CREATE TABLE train_rides (
    trip_id bigserial PRIMARY KEY,
    origination text NOT NULL,
    destination text NOT NULL,
    departure timestamp with time zone NOT NULL,
    arrival timestamp with time zone NOT NULL
);

INSERT INTO train_rides (origination, destination, departure, arrival)
VALUES
    ('Chicago', 'New York', '2017-11-13 21:30 CST', '2017-11-14 18:23 EST'),
    ('New York', 'New Orleans', '2017-11-15 14:15 EST', '2017-11-16 19:32 CST'),
    ('New Orleans', 'Los Angeles', '2017-11-17 13:45 CST', '2017-11-18 9:00 PST'),
    ('Los Angeles', 'San Francisco', '2017-11-19 10:10 PST', '2017-11-19 21:24 PST'),
    ('San Francisco', 'Denver', '2017-11-20 9:10 PST', '2017-11-21 18:38 MST'),
    ('Denver', 'Chicago', '2017-11-22 19:10 MST', '2017-11-23 14:50 CST');

当我对该数据运行以下查询时：

SELECT origination || ' to ' || destination AS segment,
       to_char(departure, 'YYYY-MM-DD HH12:MI a.m. TZ') AS departure,
       to_char(arrival, 'YYYY-MM-DD HH12:MI a.m. TZ') AS arrival
FROM train_rides;

它提供了以下输出：

--------------------------------------------------------------------------------------
| segment                    | departure                 | arrival                   |
--------------------------------------------------------------------------------------
| Chicago to New York        | 2017-11-13 09:30 p.m. CST | 2017-11-14 05:23 p.m. CST |
| New York to New Orleans    | 2017-11-15 01:15 p.m. CST | 2017-11-16 07:32 p.m. CST |
| New Orleans to Los Angeles | 2017-11-17 01:45 p.m. CST | 2017-11-18 11:00 a.m. CST |
| San Francisco to Denver    | 2017-11-20 11:10 a.m. CST | 2017-11-21 07:38 p.m. CST |
| Denver to Chicago          | 2017-11-22 08:10 p.m. CST | 2017-11-23 02:50 p.m. CST |
--------------------------------------------------------------------------------------

所有时间都显示在CST时区中，该时区基于服务器时区设置

首选输出

我希望输出反映每个出发地或目的地城市的本地时区，如下所示：

--------------------------------------------------------------------------------------
| segment                    | departure                 | arrival                   |
--------------------------------------------------------------------------------------
| Chicago to New York        | 2017-11-13 09:30 p.m. CST | 2017-11-14 06:23 p.m. EST |
| New York to New Orleans    | 2017-11-15 02:15 p.m. EST | 2017-11-16 07:32 p.m. CST |
| New Orleans to Los Angeles | 2017-11-17 01:45 p.m. CST | 2017-11-18 09:00 a.m. PST |
| San Francisco to Denver    | 2017-11-20 09:10 a.m. PST | 2017-11-21 06:38 p.m. MST |
| Denver to Chicago          | 2017-11-22 07:10 p.m. MST | 2017-11-23 02:50 p.m. CST |
--------------------------------------------------------------------------------------

我如何让每个时间都反映当地时区？例如，在上面的第一行中，芝加哥的出发显示为CST，纽约的到达显示为EST

一种可能的解决方案是在时区使用

限定符，可能使用如下查找表：
----------------------------
| city          | local_tz |
----------------------------
| Chicago       | CST      |
| Denver        | MST      |
| Los Angeles   | PST      |
| New Orleans   | CST      |
| New York      | EST      |
| San Francisco | PST      |
----------------------------

我曾考虑过使用plpgsql代码块构建动态查询，但那会非常混乱。我真的希望有一种更简单、更优雅的方法来做到这一点。
我找到了一种方法来获得想要的结果；这不是最优雅的方法，但确实有效
首先，我在train_rides表中添加了两个附加列：
-- Add columns to hold local times 
ALTER TABLE train_rides
    ADD COLUMN departure_local TIMESTAMP WITHOUT TIME ZONE,
    ADD COLUMN arrival_local TIMESTAMP WITHOUT TIME ZONE;

然后，我使用一堆代码（使用不那么优雅的蛮力方法）填充LocalExample列：
接下来，我以相同的方式填充本地到达者：
-- Update arrivals to reflect local times
UPDATE train_rides
    SET arrival_local = arrival AT TIME ZONE 'US/Central'
    WHERE origination = 'Chicago';
UPDATE train_rides
   SET arrival_local = arrival AT TIME ZONE 'US/Mountain'
   WHERE origination = 'Denver';
UPDATE train_rides
    SET arrival_local = arrival AT TIME ZONE 'US/Pacific'
    WHERE origination = 'Los Angeles';
UPDATE train_rides
    SET arrival_local = arrival AT TIME ZONE 'US/Central'
    WHERE origination = 'New Orleans';
UPDATE train_rides
   SET arrival_local = arrival AT TIME ZONE 'US/Eastern'
   WHERE origination = 'New York';
UPDATE train_rides
   SET arrival_local = arrival AT TIME ZONE 'US/Pacific'
   WHERE origination = 'San Francisco';

最后，我可以使用一些SQL魔术来获得最终结果：
SELECT origination || ' to ' || destination AS segment,
       to_char(departure_local, 'YYYY-MM-DD HH12:MI a.m. ') ||
       (SELECT local_tz from local_timezones tz
           WHERE tr.origination = tz.city) AS departure,
       to_char(arrival_local, 'YYYY-MM-DD HH12:MI a.m. ') ||
       (SELECT local_tz from local_timezones tz
           WHERE tr.destination = tz.city) AS arrival
FROM train_rides tr;

如果有一种方法可以使用查找动态填充AT TIME ZONE参数，那么所有这些UPDATE语句都可以减少到只有两个。这种蛮力方法无法很好地扩展，因为我们必须为每个可能的城市手动编写代码
除非，也就是说，有人知道更好的方法。
今天我了解了SQL子查询的威力，我的脑子里突然亮起了灯泡。下面是两个更好的方法
这两种方法都使用以下名为trains\u local\u timezones
的查找表：
-----------------------------------------
| city          | timezone    | tz_abbr |
-----------------------------------------
| Chicago       | US/Central  | CST     |
| Denver        | US/Mountain | MST     |
| Los Angeles   | US/Pacific  | PST     |
| New Orleans   | US/Central  | CST     |
| New York      | US/Eastern  | EST     |
| San Francisco | US/Pacific  | PST     |
-----------------------------------------


--更好的方法（这可以根据需要扩展）

--最佳方式（无需额外列）
不同的是，我会在数据库中使用带有时区的时间戳
，其他一切都可以。然后，查询的结果是一个不带时区的时间戳
，这更有意义，因为它表明时间戳将被理解为位于起始列指定的时区中。
-----------------------------------------
| city          | timezone    | tz_abbr |
-----------------------------------------
| Chicago       | US/Central  | CST     |
| Denver        | US/Mountain | MST     |
| Los Angeles   | US/Pacific  | PST     |
| New Orleans   | US/Central  | CST     |
| New York      | US/Eastern  | EST     |
| San Francisco | US/Pacific  | PST     |
-----------------------------------------

-- Add columns to hold local times
ALTER TABLE train_rides
    ADD COLUMN departure_local TIMESTAMP WITHOUT TIME ZONE,
    ADD COLUMN arrival_local TIMESTAMP WITHOUT TIME ZONE;

-- Update departures to reflect local times
UPDATE train_rides
   SET departure_local = departure AT TIME ZONE
   (SELECT timezone from trains_local_timezones tz
     WHERE origination = tz.city);

-- Update arrivals to reflect local times
UPDATE train_rides
   SET arrival_local = arrival AT TIME ZONE
   (SELECT timezone from trains_local_timezones tz
     WHERE destination = tz.city);


SELECT origination || ' to ' || destination AS segment,
       to_char(departure_local, 'YYYY-MM-DD HH12:MI AM ') ||
       (SELECT tz_abbr from trains_local_timezones tz
           WHERE tr.origination = tz.city) AS local_departure,

       to_char(arrival_local, 'YYYY-MM-DD HH12:MI AM ') ||
       (SELECT tz_abbr from trains_local_timezones tz
           WHERE tr.destination = tz.city) AS local_arrival
FROM train_rides tr;

SELECT origination || ' to ' || destination AS segment,
       to_char(departure AT TIME ZONE
           (SELECT timezone from trains_local_timezones tz
            WHERE origination = tz.city), 'YYYY-MM-DD HH12:MI AM ') ||
       (SELECT tz_abbr from trains_local_timezones tz
           WHERE tr.origination = tz.city) AS local_departure,
       to_char(arrival AT TIME ZONE
           (SELECT timezone from trains_local_timezones tz
            WHERE destination = tz.city), 'YYYY-MM-DD HH12:MI AM ') ||
       (SELECT tz_abbr from trains_local_timezones tz
           WHERE tr.destination = tz.city) AS local_arrival
FROM train_rides tr;