Then, the view loops through each of these to provide the value of each column in the database.

然后，该视图通过在列表中的每个列上进行循环，提供数据库中每一列的值。

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This timestamp column is maintained by default by the database manager, but a user-provided input value is also accepted.

该时间戳列默认情况下由数据库管理器维护，但是也接受用户提供的输入值。

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Additional code could be added to perform a check to see if the new value is a user-defined value indicating that the database value should be set to NULL or the default value defined for the column.

可以添加额外的代码来执行一个检查，检查新值是不是一个用户定义值，用以表明数据库值应该被设置为NULL或针对该列定义的默认值。

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