原因：定义的某些基本例没有给出自己的类，然后以这种方法定义了递归数据类型。
Cause: The recursive datatype is defined in such a way that certain base cases of the definition are not given their own classes.
这种新的数据类型的优点是，它允许使用一条SELECT语句和传统的操作符（而不需要使用递归）在层次中进行搜索。
The advantage to this new data type is that it allows for searches within the hierarchy with a single SELECT statement, using traditional operators without recursion.
这种类型的错误是这样产生的：定义的某些基本例没有被给出它们自己的类，然后以这种方法定义了一个递归的数据类型。
Bugs of this sort result from defining a recursive datatype in such a way that certain base cases of the definition are not given their own classes.
递归成员中列的数据类型必须与定位点成员中相应列的数据类型一致。
The data type of a column in the recursive member must be the same as the data type of the corresponding column in the anchor member.
递归成员中列的数据类型必须与定位点成员中相应列的数据类型一致。
The data type of a column in the recursive member must be the same as the data type of the corresponding column in the anchor member.
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