添加一个ORDER SIBLINGS BY子句，该子句只能与分级查询子句组合使用，并且将按预先定义的顺序返回同级查询结果。
Adding an ORDER siblings BY clause which is only allowed in composition with the hierarchical query clause and will return the siblings in the predefined sequence.
伪列是具有预先定义的名称的标识符，其中包含关于分级查询的信息；它的用途类似于表中的任何列。
A pseudo column is an identifier with a predefined name that holds information about the hierarchical query and that can be used like any column in a table.
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