PostgreSQL 9.5 的最近日期时间答案

【问题标题】：Closest datetime for PostgreSQL 9.5PostgreSQL 9.5 的最近日期时间
【发布时间】：2016-12-03 15:54:35
【问题描述】：

我使用的是 PostgreSQL 9.5 我有一张这样的桌子：

CREATE TABLE tracks ( 
    track                bigserial  NOT NULL,
    time_track           timestamp,
    CONSTRAINT pk_aircraft_tracks PRIMARY KEY ( track )
 );

我想通过 SELECT 运算符获取最接近的日期时间值。例如，如果我有：

  track    datatime
    1 | 2016-12-01 21:02:47 
    2 | 2016-11-01 21:02:47
    3 |2016-12-01 22:02:47

对于输入数据时间 2016-12-01 21:00，轨道为 2。

我发现了Is there a postgres CLOSEST operator? 类似的整数问题。但它不适用于数据时间或 PostgreSQL 9.5：

SELECT * FROM
(
  (SELECT time_track, track FROM tracks WHERE time_track >= now() ORDER BY time_track LIMIT 1) AS above
  UNION ALL
  (SELECT time_track, track FROM tracks WHERE time_track < now() ORDER BY time_track DESC LIMIT 1) AS below
) 
ORDER BY abs(?-time_track) LIMIT 1;

错误：

ERROR:  syntax error at or near "UNION"
LINE 4:   UNION ALL

【问题讨论】：

AS above 和 AS below 是多余的。

标签： postgresql datetime

【解决方案1】：

Track 1 最接近'2016-12-01 21:00'：

with tracks(track, datatime) as (
values
    (1, '2016-12-01 21:02:47'::timestamp),
    (2, '2016-11-01 21:02:47'),
    (3, '2016-12-01 22:02:47')
)

select *
from tracks
order by
    case when datatime > '2016-12-01 21:00' then datatime - '2016-12-01 21:00' 
    else '2016-12-01 21:00' - datatime end
limit 1;

 track |      datatime       
-------+---------------------
     1 | 2016-12-01 21:02:47 
(1 row)

【讨论】：