postgresql – 在聚合函数之前对分组行进行排序

我有一个带点几何的postgis表.

点数表：

id | uid | date | geom

具有相同uid的点是相同的目标.我正在尝试使用ST_MakeLine的GROUP BY uid创建一个完整的目标Linestring.

SELECT uid,ST_MakeLine(geom)
FROM points
GROUP BY uid

这有效,但我想确保点的顺序正确.
我试着通过在分组之前添加ORDER BY日期来做到这一点.

SELECT uid,ST_MakeLine(geom)
FROM points
ORDER BY date <-- does not work
GROUP BY uid

ERROR: Syntax error at or near "GROUP"

有没有办法在分组行输入聚合函数之前对其进行排序？

解决方法

ORDER BY子句可以放在聚合参数的末尾.

SELECT uid,ST_MakeLine(geom ORDER BY date)
FROM points
GROUP BY uid

http://www.postgresql.org/docs/9.1/static/sql-expressions.html#SYNTAX-AGGREGATES