Updatable Join Views (181)

A join view is defined as a view that has more than one table or view in its FROM
clause (a join) and that does not use any of these clauses: DISTINCT, aggregation,
GROUP BY, START WITH, CONNECT BY, ROWNUM, and set operations (UNION ALL,
INTERSECT, and so on).

An updatable join view is a join view that involves two or more base tables or views,
where UPDATE, INSERT, and DELETE operations are permitted. The data dictionary
views ALL_UPDATABLE_COLUMNS, DBA_UPDATABLE_COLUMNS, and USER_UPDATABLE_COLUMNS
contain information that indicates which of the view columns
are updatable. In order to be inherently updatable, a view cannot contain any of the
following constructs:

■ A set operator
■ A DISTINCT operator
■ An aggregate or analytic function
■ A GROUP BY, ORDER BY, CONNECT BY, or START WITH clause
■ A collection expression in a SELECT list
■ A subquery in a SELECT list
■ Joins (with some exceptions)
Views that are not updatable can be modified using INSTEAD OF triggers.

可更新的连接视图
1. 连接视图指在一个视图的定义查询的 FROM 字句中引用了多个表或视图 ,且查询中没有使用以下子句：DISTINCT,聚合函数等.
2. 可更新连接视图是指涉及到两张或以上的表进行DML操作是被允许的
3. 从ALL_UPDATABLE_COLUMNS, DBA_UPDATABLE_COLUMNS等字典视图中可查询出哪些视图列是可被更新的
4. 包含以下运算结构的视图不能更新 :set , disitnct 等
5. 对于不可更新的视图,可以利用 INSTEAD OF 触发器对其数据进行修改

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