Designating the node level v16
LEVEL is a pseudo-column that you can use wherever a column can appear in the
SELECT command. For each row in the result set,
LEVEL returns a non-zero integer value designating the depth in the hierarchy of the node represented by this row. The
LEVEL for root nodes is 1. The
LEVEL for direct children of root nodes is 2, and so on.
The following query is a modification of the previous query with the addition of the
LEVEL pseudo-column. In addition, using the
LEVEL value, the employee names are indented to further emphasize the depth in the hierarchy of each row.
The output from this query is:
Nodes that share a common parent and are at the same level are called siblings. For example, in the above output, employees
JAMES are siblings since they are all at level three with parent
CLARK are siblings since they are at level two and
KING is their common parent.
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