如果DML sql语句、触发器、视图或例程内引用了一个全局变量，将为语句或对象记录关于完全限定全局变量名的依赖关系。

When a global variable is referenced within a DML SQL statement or within a trigger, view or routine, a dependency on the fully-qualified global variable name is recorded for the statement or object.

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如果存在某个变量名既是全局变量又是节块变量，那么会优先使用节块变量值。

If a variable exists both as a global and in a section, the section variable is used.

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