minor updates to ST_MakeLine to clarify pre-9.0 and 9.0+ approaches

git-svn-id: http://svn.osgeo.org/postgis/trunk@7684 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/reference_constructor.xml b/doc/reference_constructor.xml
index 433db0c86415e0a2c521ad6114b4bfd7e6e1c3c5..7fcb254749f73456b82c77b29a4a2f43827f7ba8 100644 (file)
--- a/doc/reference_constructor.xml
+++ b/doc/reference_constructor.xml
@@ -1221,6 +1221,8 @@ BOX3D(-989502.1875 528439.5625 10,-987121.375 529933.1875 10)
                        in the order of the travel.</para>
 
                <programlisting>
+-- For pre-PostgreSQL 9.0 - this usually works, 
+-- but the planner may on occasion choose not to respect the order of the subquery
 SELECT gps.gps_track, ST_MakeLine(gps.the_geom) As newgeom
        FROM (SELECT gps_track,gps_time, the_geom
                        FROM gps_points ORDER BY gps_track, gps_time) As gps
@@ -1229,7 +1231,8 @@ SELECT gps.gps_track, ST_MakeLine(gps.the_geom) As newgeom
                <programlisting>
 -- If you are using PostgreSQL 9.0+ 
 -- (you can use the new ORDER BY support for aggregates)
--- this is a more guaranteed way to get ordered linestring
+-- this is a guaranteed way to get a correctly ordered linestring
+-- Your order by part can order by more than one column if needed
 SELECT gps.gps_track, ST_MakeLine(gps.the_geom ORDER BY gps_time) As newgeom
        FROM gps_points As gps
        GROUP BY gps.gps_track;</programlisting>