Unlike a table, a view is not allocated any storage space, nor does a view actually
contain data. Rather, a view is defined by a query that extracts or derives data from the
tables that the view references. These tables are called base tables. Base tables can in
turn be actual tables or can be views themselves (including materialized views).
Because a view is based on other objects, a view requires no storage other than storage
for the definition of the view (the stored query) in the data dictionary.
1. 视图不占用任何存储空间 , 不包含实际的数据
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