Detect hierarchy loops with Oracle 10g's new hierarchy pseudocolumns

In a previous tip, I described how to sort the entries in a hierarchical query. For a hierarchical query to work, however, the data must not loop back upon itself. That is, a parent row may not list itself or one of its child rows as its own parent. If this were the case, Oracle could follow the links around and around, never coming to a definitive end.

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