postgresql - JOIN 结果的顺序

Question

我有这个问题

SELECT orden.id,
array_to_string(array_agg(observaciones.fecha_hora),'<br>') as observaciones
FROM orden
LEFT JOIN observacion observaciones ON observaciones.orden_id = orden.id
GROUP BY orden.id

它返回这个:

orden.id = 5878  
observaciones
2012-03-15 01:39:11
2012-03-15 01:40:28
2012-03-15 01:40:42
2012-03-15 09:09:08
2012-03-15 09:11:10
2012-03-15 01:18:34
2012-03-15 01:19:27
2012-03-15 09:17:01
2012-03-15 09:17:36
2012-03-15 03:16:58
2012-03-15 01:21:01
2012-03-15 03:17:06
2012-03-15 03:17:26
2012-03-15 01:27:33
2012-03-15 03:18:05
2012-03-15 03:24:56
2012-03-15 03:49:24
2012-03-15 01:27:43
2012-03-15 01:38:30
2012-03-15 06:30:13

问题是，我怎样才能按 DESC 顺序获取这些日期时间我不能做子查询，因为我正在优化一个旧查询，我真的需要一个 JOIN。我正在使用 postgresql。

Answer 1

最后我这样做了...

    SELECT 
    orden.id,
    array_to_string(array_agg(observaciones.fecha_hora),'<br>') as observaciones
    FROM orden
    LEFT JOIN (
        SELECT orden_id, fecha_hora FROM observacion ORDER BY fecha_hora DESC
    ) as observaciones ON observaciones.orden_id = orden.id
    GROUP BY orden.id

感谢大家..