title: ArangoDB AQL: Traverse all graph edges without using startVertex
body: <p>I have a scenario where I would like to loop over all the edges in an edge collection (1-depth traversal). Thus, in the query below, I don't want to specify the startVertex.</p>
  
  <pre><code>[WITH vertexCollection1[, vertexCollection2[, ...vertexCollectionN]]]
  FOR vertex[, edge[, path]]
    IN [min[..max]]
    OUTBOUND|INBOUND|ANY startVertex
    GRAPH graphName
    [PRUNE pruneCondition]
    [OPTIONS options]
  </code></pre>
  
  <p>However, it seems this isn't possible. Is there some way to go about this? I know I could just perform a normal loop over the edge collection and retrieve the _from and _to vertices for each edge, but I'm worried about performance issues if I do this. I would appreciate any advice, especially for improving performance.</p>