passingby 子句建立了SQL和XQuery上下文间的绑定。
The passing by clause establishes the binding between the SQL and the XQuery context.
多数情况下按照上述方法使用XQuery中的变量，即通过for子句隐式建立变量，而不是使用let子句显式地定义变量。
You most often will use variables in XQuery as shown above, though, where the variable is created implicitly by a for clause, rather than explicitly with a let clause.
其思想是，在一个描述性级别上，在FROM 子句中建立一个临时表，这个表由在调用任何空间函数之前导入的数据组成。
The idea is, on a descriptive level, to build in the FROM clause a temporary table that consists of the data to be imported before calling any of the spatial functions.
其思想是，在一个描述性级别上，在FROM 子句中建立一个临时表，这个表由在调用任何空间函数之前导入的数据组成。
The idea is, on a descriptive level, to build in the FROM clause a temporary table that consists of the data to be imported before calling any of the spatial functions.
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