数据库视图是否会影响查询性能？这个问题的出现原因是因为不同的关系型数据库管理系统（RDBMS）处理数据库视图的方式不同。一般来说，数据库视图只是一种简化查询的便捷方式，没有进行优化。然而，一些数据库系统使用了"materialized views"（物化视图），这种视图使用了缓存机制，可以提高查询性能。

解决方法就是使用物化视图来替代普通的数据库视图。物化视图是一种预先计算和存储查询结果的机制，可以提高查询性能。在使用物化视图时，数据库系统会定期或根据需要自动更新视图的数据，确保数据的准确性。

下面是一个使用物化视图的示例代码（使用Oracle数据库）：

CREATE MATERIALIZED VIEW mv_example
BUILD IMMEDIATE
REFRESH COMPLETE
AS
SELECT column1, column2, aggregate_function(column3)
FROM table
GROUP BY column1, column2;

在上面的示例中，创建了一个名为"mv_example"的物化视图，它会立即构建并完全刷新。视图的数据来源于"table"表，并使用了"column1"和"column2"进行分组，同时对"column3"进行了聚合函数计算。

使用物化视图的好处是，当查询需要从视图中获取数据时，数据库系统可以直接返回物化视图中存储的预先计算好的结果，而不需要再次执行复杂的查询操作。这样可以大大提高查询性能，尤其是对于复杂的查询和大型数据集。

，数据库视图是否会影响查询性能取决于所使用的RDBMS。一般来说，普通的数据库视图只是简化查询的便捷方式，不会进行优化。然而，使用物化视图可以提高查询性能，通过预先计算和存储查询结果来避免重复的查询操作。通过合理使用物化视图，可以显著提升查询性能，特别是在处理复杂查询和大型数据集时。

由于需要将两个视图连接在一起，所以在视图内运行的某个查询与在视图外运行的相同查询应该具有相同的性能。但是，当您需要将两个视图连接在一起时，事情会变得更加复杂。您可能会将不需要的表引入查询中，或者冗余地引入表。数据库优化器可能会在创建良好的查询执行计划方面遇到更多问题。因此，尽管视图在允许更精细的安全性等方面非常好，但对于模块化来说，它们并不一定是好的选择。

解决方法：

There are a few ways to address the performance issues that can arise when using views. One approach is to carefully design the views so that they only include the necessary tables and columns. This can help to prevent bringing in unnecessary data and improve query performance. Additionally, using the "WITH SCHEMABINDING" option when creating a view can help to ensure that the underlying tables and columns cannot be modified in a way that would break the view.

Another approach is to use indexed views, which can significantly improve the performance of queries that utilize the view. Indexed views essentially create a physical copy of the view's result set, allowing for faster querying and reducing the need for joins and other operations.

Finally, it may be necessary to rewrite queries that utilize views in order to optimize performance. This could involve rewriting the query to eliminate unnecessary joins or filters, or restructuring the logic of the query to improve efficiency. It may also be beneficial to use query hints or other optimization techniques to guide the database optimizer in creating a more efficient query execution plan.

Overall, while views can be a useful tool for organizing and securing data, they can also introduce performance challenges. By carefully designing views, using indexed views, and optimizing queries, it is possible to mitigate these challenges and improve overall query performance.

Do database views affect query performance?

数据库视图对查询性能有影响吗？

Views are often considered as read-only Stored Procedures. They provide the database with as much information as possible in advance to optimize pre-compilation.

通常视图被认为是只读的存储过程。它们会提供尽可能多的信息给数据库，以便进行预编译和优化。

Views can also be indexed, allowing for optimized access to the desired data for specific types of queries.

视图也可以创建索引，以便针对特定类型的查询实现对数据的优化访问。

However, it is questioned whether views actually provide a performance advantage over equivalent select statements. While indexes can certainly improve performance, they also benefit select statements. So, the question arises whether views are inherently faster, or if there is any concrete evidence to support this claim.

然而，有人质疑视图是否真的比等效的select语句提供了性能优势。虽然索引可以明显提升性能，但它们也对select语句有所帮助。因此，人们开始怀疑视图是否本质上更快，或者是否有任何确凿的证据来支持这一观点。

It should be noted that no DB server creates a query execution plan at the time of view or stored procedure creation. Execution plans require index statistics, which are not available at compile time. The compilation process simply transforms the SQL/DDL into an internal format.

需要注意的是，没有任何数据库服务器会在视图或存储过程创建时生成查询执行计划。执行计划需要索引统计数据，这些数据在编译时是不可用的。编译过程只是将SQL/DDL转换为内部格式。

However, some DB servers do support "indexed views," which are similar to "materialized views." These indexed views are closer to automatically maintained tables rather than traditional views.

然而，一些数据库服务器支持"索引视图"，这些视图类似于"物化视图"。这些索引视图更接近于自动维护的表，而不是传统的视图。

In conclusion, the impact of database views on query performance is still a topic of debate. While views can be optimized through indexing, it is unclear whether they inherently provide faster performance compared to equivalent select statements. Further research and experimentation may be necessary to determine the true impact of views on query performance.

数据库视图对查询性能的影响仍然是一个有争议的话题。虽然视图可以通过索引进行优化，但是目前尚不清楚它们本质上是否相对于等效的select语句提供更快的性能。需要进一步的研究和实验来确定视图对查询性能的真实影响。