MySQL 物化视图综合指南-mysql教程-PHP中文网

MySQL 中的物化视图：可以做到吗？

物化视图是数据库管理中的一项重要功能，可以显着提高查询性能和数据检索效率。虽然 MySQL 不像其他一些数据库系统那样本身支持物化视图，但有一些有效的解决方法可以实现类似的功能。本文深入探讨了什么是物化视图、它们的优点以及如何在 MySQL 中实现它们。

什么是物化视图？

物化视图是包含查询结果的数据库对象。与每次查询时动态生成结果的标准视图不同，物化视图物理存储查询结果数据，从而提高复杂和资源密集型查询的性能。

物化视图的主要优点

物化视图存储查询结果，减少重复执行复杂查询的需要。
它们允许更快的数据检索，这对于大型数据集和实时应用程序至关重要。
通过缓存查询结果，物化视图减少了数据库服务器的负载。

让我们用这个图来解释物化视图的概念：

A Comprehensive Guide to Materialized Views in MySQL

基表：在图的左侧，我们有两个矩形，标记为“基表 A”和“基表 B”。这些代表包含原始数据的原始数据库表。
查询：在中间，我们有一个标记为“查询”的矩形。这表示在基表上执行的查询或一组操作以派生特定结果集。
物化视图：在右侧，我们有一个标记为“物化视图”的矩形。这是我们正在说明的关键概念。

物化视图是包含查询结果的数据库对象。与每次访问时运行查询的常规视图不同，物化视图像表一样物理存储结果集。这有几个优点：

性能：对于复杂查询，尤其是涉及大型数据集或多个联接的查询，物化视图可以显着提高查询性能，因为结果是预先计算的。
数据仓库和 OLAP：它们在数据仓库和 OLAP（在线分析处理）场景中特别有用，在这些场景中，您可能会进行复杂的聚合或计算，而即时计算的成本很高。

箭头：图中的箭头显示了数据的流动。从基表到查询的箭头表示正在处理的原始数据。从查询到物化视图的箭头表示正在存储的结果。
刷新：底部标有“刷新”的弯曲箭头是理解物化视图的关键部分。由于基表中的数据可能会随着时间的推移而变化，因此需要定期更新或“刷新”物化视图以反映这些变化。此刷新可以设置为按特定时间间隔自动发生，也可以在需要时手动完成。

物化视图需要在查询性能和数据新鲜度之间进行权衡。它们提供快速的查询结果，但代价是刷新之间可能会出现稍微过时的数据。

在 MySQL 中实现物化视图

虽然MySQL本身不支持物化视图，但您可以使用表和触发器的组合来实现它们。以下是有关如何在 MySQL 中创建物化视图的分步指南：

第 1 步：创建基表

首先，创建一个用于存储物化视图数据的基表。

<span>CREATE TABLE materialized_view AS</span><br>
<span>SELECT column1, column2, aggregate_function(column3)</span><br>
<span>FROM base_table</span><br>
<span>GROUP BY column1, column2;</span>

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第 2 步：设置触发器来维护物化视图

为了确保物化视图与基表保持同步，您需要为 INSERT、UPDATE 和 DELETE 操作创建触发器。

插入触发器

<span>CREATE TRIGGER trg_after_insert AFTER INSERT ON base_table</span><br>
<span>FOR EACH ROW</span><br>
<span>BEGIN</span><br>
<span>    INSERT INTO materialized_view (column1, column2, column3)</span><br>
<span>    VALUES (NEW.column1, NEW.column2, NEW.column3);</span><br>
<span>END;</span>

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更新触发器

<span>CREATE TRIGGER trg_after_update AFTER UPDATE ON base_table</span><br>
<span>FOR EACH ROW</span><br>
<span>BEGIN</span><br>
<span>    UPDATE materialized_view</span><br>
<span>    SET column1 = NEW.column1, column2 = NEW.column2, column3 = NEW.column3</span><br>
<span>    WHERE id = OLD.id;</span><br>
<span>END;</span>

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删除触发器

<span>CREATE TRIGGER trg_after_delete AFTER DELETE ON base_table</span><br>
<span>FOR EACH ROW</span><br>
<span>BEGIN</span><br>
<span>    DELETE FROM materialized_view WHERE id = OLD.id;</span><br>
<span>END;</span>

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第 3 步：刷新物化视图

根据应用程序的要求，您可能需要定期刷新物化视图以确保它反映最新的数据。这可以使用计划的事件或 cron 作业来完成。

预定活动示例

<span>CREATE EVENT refresh_materialized_view</span><br>
<span>ON SCHEDULE EVERY 1 HOUR</span><br>
<span>DO</span><br>
<span>BEGIN</span><br>
<span>    TRUNCATE TABLE materialized_view;</span><br>
<span>    INSERT INTO materialized_view (column1, column2, aggregate_function(column3))</span><br>
<span>    SELECT column1, column2, aggregate_function(column3)</span><br>
<span>    FROM base_table</span><br>
<span>    GROUP BY column1, column2;</span><br>
<span>END;</span>

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使用快速数据库生成器的物化视图

虽然理解 SQL 和执行高效查询至关重要，但构建完整的数据库需要大量的 SQL 知识。这就是像 Five 这样的快速数据库构建器发挥作用的地方。

In Five, you can define your database schema using MySQL, including advanced operations. Five provides a MySQL database for your application and generates an automatic UI, making it easier to interact with your data.

With Five, you can create forms, charts, and reports based on your database schema. This means you can build interfaces that interact with data fields.

For example, if you have a complex query that aggregates data from multiple tables, you can create a materialized view to store the results of this query. This can significantly speed up your application by reducing the load on your database and providing quicker access to frequently queried data:

Five also allows you to write custom JavaScript and TypeScript functions, giving you the flexibility to implement complex business logic. This is crucial for applications that require more than just standard CRUD (Create, Read, Update, Delete) operations.

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A Comprehensive Guide to Materialized Views in MySQL — An example application built on a MySQL database using Five

Considerations For Materialized Views in MySQL

Storage: Materialized views consume additional storage space. Ensure that your database has adequate space to accommodate the materialized views.
Maintenance: Regularly maintain and refresh materialized views to ensure data consistency and accuracy.
Indexing: Use appropriate indexing on materialized view tables to further enhance query performance.

Conclusion

Although MySQL does not support them natively, you can effectively implement materialized views using tables and triggers. By understanding and utilizing materialized views, you can significantly enhance the performance and scalability of your MySQL database applications.

FAQs

Q: Does MySQL support materialized views natively?
No, MySQL does not support materialized views natively, but you can achieve similar functionality using tables and triggers.

Q: How often should I refresh my materialized view?
The refresh frequency depends on your application’s requirements. For real-time applications, you might need more frequent updates, while less frequent updates might suffice for batch processing applications.

Q: What are the alternatives to materialized views in MySQL?
Alternatives include using temporary tables, cache tables, or optimizing queries through indexing and query restructuring.

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