- a relationship exists between rows in the same table
=> a kind of self-join
- restriction: SELECT can NOT contain a join or query of join
- tree walking: null이 나올 때까지
* Clauses
- START WITH: starting point of tree walking
CAN contain a subquery
omitted, all row are considered as root rows
- CONNECT BY: direction of tree-walking
can NOT contain a subquery
- PRIOR: Parent Row
can be in connect by and select-list clauses
can be in either side of condition
* Hierarchical Query Pseudocolumn
- LEVEL
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