The IMPLICITLY HIDDEN attribute on a CREATE or ALTER TABLE statement specifies that the column is not visible in SQL statements unless the column is explicitly referenced by name.

CREATE或ALTER table语句中的IMPLICITLY hidden属性表示，除非根据名称显式引用列，否则该列在sql语句中不可见。

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All referenced documents in this specification refer to the latest revision level unless otherwise stated.

除非另有说明，否则本规范中的所有参考文件均指代最新修订版。

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Thus, global variables cannot be directly assigned a value within a function (unless named in a global statement), although they may be referenced.

因此，全局参数虽然可以被引用，但它们不能在函数中直接赋值（除非它们用global 语句命名）。

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