Defining the parent/child relationship v16
To determine the children for any given row:
parent_expron the given row.
child_expron any other row resulting from the evaluation of
parent_expr = child_expr, then this row is a child node of the given parent row.
Repeat the process for all remaining rows in
table_expression. All rows that satisfy the equation in step 3 are the children nodes of the given parent row.
The evaluation process to determine if a row is a child node occurs on every row returned by
table_expression before the
WHERE clause is applied to
Iteratively repeating this process, treating each child node found in the prior steps as a parent, constructs an inverted tree of nodes. The process is complete when the final set of child nodes has no children of its own. These are the leaf nodes.
SELECT command that includes a
CONNECT BY clause typically includes the
START WITH clause. The
START WITH clause determines the rows that are to be the root nodes, that is, the rows that are the initial parent nodes upon which to apply the algorithm.