Hierarchical Queries: Connect by
The connect by clause is used to query hierarchies if they are stored as parent-child relationships, also known as an adjacency lists model. Simply speaking, this model means that a parent – child pair is stored for each child. In general adjacency lists can represent directed graphs, not only hierarchy trees; in this case the list describes the set of neighbors of a vertex in the graph. So an adjacency list model is much wider and a parent-child model is one of its implementations.