Overview of Views (174)

A view is a tailored presentation of the data contained in one or more tables or other
views. A view takes the output of a query and treats it as a table. Therefore, a view can
be thought of as a stored query or a virtual table. You can use views in most places
where a table can be used.

Because views are derived from tables, they have many similarities. For example, you
can define views with up to 1000 columns, just like a table. You can query views, and
with some restrictions you can update, insert into, and delete from views. All
operations performed on a view actually affect data in some base table of the view and
are subject to the integrity constraints and triggers of the base tables.
You cannot explicitly define triggers on views, but you can define them for the
underlying base tables referenced by the view. Oracle does support definition of
logical constraints on views.

檢視
1. 檢視是將一個或多個表中的資料進行整理後展現出來 , 可以當作一個表的查詢輸出
2. 檢視可看做儲存的查詢和虛擬表
3. 檢視和表有很多相似的地方 , 如最多可定義1000列 .
4. 對檢視的進行dml操作將反應到基表中 .

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