[Qgis-user] "Dissolve" a line layer?

[jamesh]

sorry to ask even simpler questions,
I am using spatialite_gui.
I  want to do the same merge as described above to merge streets with the
name name, that are within 50m of each other into one line, I have imported
a shapefile called NZRoadCentrelines12414 ( from OSM then edited some
attributes in QGIS) am running the following code in the sql window

SELECT addgeometrycolumn('roads_merged', 'Geometry', 4326,
'MULTILINESTRING', 'XY');
INSERT INTO roads_merged (road_id, road_name, Geometry) 
        SELECT road_id, road_name, CastToMulti(GUnion(Geometry))
        FROM roads
        GROUP BY road_name;

when I run this I get 1 result = 0

<http://osgeo-org.1560.x6.nabble.com/file/n5134740/wert.jpg> 
I don't see where the code selects the data from my original table  ?
can you advise what a spatial_gui user should do in this case.
Thankyou





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