title: How can I get all property keys, for all nodes or for a given label, with Cypher/Neo4J?
body: <p>Neo4j has recently introduced <code>call db.labels();</code>, which yields all labels used in the database, presumably without the need to do a full scan.</p>
  
  <p>Is there something similar for property keys, ie, some instruction to return all keys used in the DB, whatever the nodes? And is there something parameterized on the label, i.e.,  returning all the keys used in at least one node having a given label?</p>
  
  <p>Again, I know how to do either query with full scans, but I'm afraid they won't be efficient. I know that such a function must be the one used by the web browser to show all property keys on a left column.</p>