Let's take the following query:
MATCH ()-[r]-()
RETURN r
When we write these kinds of queries, we are actually performing what is called pattern matching with graph databases. The following schema explains this concept:
In this scenario, we have a directed graph made of nodes with labels A or B. We are looking for the sequence A -> B. Pattern matching consists of moving a stencil along the graph and seeing which pairs of nodes and relationships are consistent with it. On the first iteration, both the node labels and the relationship direction matches the search pattern. But on the second and third iterations, the node labels are not the expected ones, and these patterns are rejected. On iteration four, the labels are right, but the relationship orientation is reversed, which makes the matching fail again. Finally, on the last iteration, the pattern is respected even if not drawn in the right order: we have a node A connected with an outbound relationship to a...
