pgRouting shortest_path得到潮頭osm_id值

Question

我有SQL：

SELECT osm_id, vertex_id 
    FROM ways 
    JOIN 
    (SELECT * FROM shortest_path(' 
     SELECT gid AS id, 
      source::int4 AS source, 
      target::int4 AS target, 
      length::float8 AS cost 
     FROM ways', 
     7856, 
     18774, 
     false, 
     false)) AS route 
    ON 
    ways.gid = route.edge_id 
    order by vertex_id 

它生產的是這樣的：

osm_id;vertex_id 
5024380;6223 
5024380;6224 
5024380;6225 
5024380;6226 
175339584;6227 
5024380;6230 
5024380;6231 
5024380;6232 
38521651;6233 
5024380;6234 

你可以看到，osm_id不是唯一的。我neet osm_id訂購vertex_id。我怎樣才能得到唯一osm_id值vertex_id排序。我不需要vertex_id列。只需要osm_id。我嘗試了group by條款，但這不起作用。休耕查詢：

SELECT distinct osm_id 
    FROM ways 
    JOIN 
    (SELECT * FROM shortest_path(' 
     SELECT gid AS id, 
      source::int4 AS source, 
      target::int4 AS target, 
      length::float8 AS cost 
     FROM ways', 
     7856, 
     18774, 
     false, 
     false)) AS route 
    ON 
    ways.gid = route.edge_id 
    --group by osm_id 
    order by vertex_id 

給出了錯誤：

ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list 
LINE 21: order by vertex_id 
        ^

********** Error ********** 

ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list 
SQL state: 42P10 
Character: 420 

Answer 1

試試這個：

SELECT osm_id 
    FROM ways 
    JOIN 
    (SELECT * FROM shortest_path(' 
     SELECT gid AS id, 
      source::int4 AS source, 
      target::int4 AS target, 
      length::float8 AS cost 
     FROM ways', 
     7856, 
     18774, 
     false, 
     false)) AS route 
    ON 
    ways.gid = route.edge_id 
    GROUP BY osm_id 
    ORDER BY min(vertex_id)