Oracle SQL Revealed: Executing Business Logic in the Database Engine

© Alex Reprintsev 2018

Alex ReprintsevOracle SQL Revealedhttps://doi.org/10.1007/978-1-4842-3372-6_5

5. Hierarchical Queries: Connect by

Alex Reprintsev¹ 

(1)

London, UK

 

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 hierarchical 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.

Listing 5-1 shows the query for building hierarchy based on a parent-child relationship and ...