SQL 按分组限制

Question

这可能不是很正确的问题标题，但未能找到更好的名称。

我有以下 table 结构：

id | lat  | lon  | trajectory_id | time
1  | 15.8 | 17.1 | 162           | 10:01
2  | 11.5 | 59.7 | 162           | 10:02
3  | 16.4 | 79.9 | 162           | 10:03
4  | 29.5 | 10.3 | 180           | 11:12
5  | 58.2 | 11.1 | 180           | 11:13
6  | 54.5 | 14.1 | 180           | 11:14
7  | 14.9 | 15.2 | 166           | 13:40
8  | 15.0 | 13.1 | 166           | 13:42

我想得到每个轨迹的第一个点（按时间排序）。这意味着：

id | lat  | lon  | trajectory_id | time
1  | 15.8 | 17.1 | 162           | 10:01
4  | 29.5 | 10.3 | 180           | 11:12
7  | 14.9 | 15.2 | 166           | 13:40

我该怎么做？我尝试按 trajectory_id 分组，然后应用限制 1，但它限制了轨迹，而不是点本身。

Answer 1

WITH CTE AS
(SELECT id,lat,lon,trajectory_id,time,
ROW_NUMBER() OVER(PARTITION BY trajectory_id ORDER BY time) rn
FROM t)
SELECT id,lat,lon,trajectory_id,time FROM CTE WHERE rn=1

Answer 2

每个 trajectory_id 使用 ROW_NUMBER() 以便仅检索每个 trajectory_id 的第一行。

select id, lat, lon, trajectory_id, time
from
(
  select 
    mytable.*, 
    row_number() over (partition by trajectory_id order by time) as rn
  from mytable
) numbered
where rn = 1;

SQL 按分组限制

SQL limit by group by

sql

postgresql

group-by

limit