Some data warehouses drop indexes on tables at night to facilitate faster loads.
However, all views dependent on the table whose index is dropped get invalidated.
This means that subsequently running any package that reference these dropped
views will invalidate the package.
Remember that whenever you create a table, index, and view, and then drop the index,
all objects dependent on that table are invalidated, including views, packages, package
bodies, functions, and procedures. This protects updatable join views.
To make the view valid again, use one of the following statements:
SELECT * FROM vtest;
or
ALTER VIEW vtest compile;

数据仓库系统中的依赖性问题
1. 有些数据仓库系统会在夜间删除表的索引以便加快数据加载速度。但是，所有依赖于被删除索引的表的视图将被置为无效状态。
而引用了这些视图的包在运行时也将被置于无效状态。