sql - 列「pedroad.id」は、GROUP BY 句に表示されるか、集計関数で使用する必要があります

Question

select di.seq, di.node , di.edge , di.cost, a.geom
from pgr_dijkstra(
    'select id, target, source, sum(cost) from pedroad', 
     array(select get_source2('location1'))
     ,array(select get_target2('test4'))
     ,false) as di, 
    pedroad a
    where di.node = a.source;

error: column "pedroad.id" must appear in the GROUP BY clause or be used in an aggregate function

どのように使用すればよいgroup byですか?