【连载】关系型数据库是如何工作的？（9）
查询管理器 查询管理是一个数据库强大与否的一个判断指标。通过查询管理，可以把一个糟糕的查询语句转换为一段快速执行的代码，代码执行后返回结果给客户端管理器。整个过程分为多步： 查询首先被解析并检查其有效性； 重写查询并删除不必要的操作，另外做一
查询管理器
查询管理是一个数据库强大与否的一个判断指标。通过查询管理，可以把一个糟糕的查询语句转换为一段快速执行的代码，代码执行后返回结果给客户端管理器。整个过程分为多步：
- 查询首先被解析并检查其有效性；
- 重写查询并删除不必要的操作，另外做一些预优化；
- 为了提升性能进行必要的优化，最终转换为一个执行计划；
- 编译执行计划；
- 最后运行执行计划。
在读了这一章节之后，如果对查询优化想更深入的理解，我推荐阅读以下资料：
- 1979年发表的一篇最早的关于基于成本优化的论文： Access Path Selection in a Relational Database Management System。这篇论文只有12页，只要具备计算机科学中级水平就可以理解。
- 关于DB 9.X如何优化查询的深度介绍：DB2 for Linux, UNIX, and Windows Optimizer。
- 一篇关于PostgreSQL如何优化查询的详细介绍：Explaining the Postgres Query Optimizer。这篇非常易于理解，因为它并不是从PostgreSQL的算法角度介绍，而是展示了PostgreSQL的查询计划。
- SQLite官方优化文档：The SQLite Query Planner。它很容易读懂，以你为SQLite优化规则很简单；但是它仅仅解释了优化器如何工作。
- SQL Server 2005优化查询的介绍：Understanding Query Processing and Query Plans in SQL Server
- Orcale 12c优化白皮书：Optimizer with Oracle Database 12c
- 《DATABASE SYSTEM CONCEPTS》的作者两篇关于查询优化的理论课程，它们主要聚焦于磁盘IO：Chapter 12: Query Processing、Chapter 13: Query Optimization
- 还有一篇我找到的更容易理解的只介绍join操作和磁盘IO的理论课程：Datenbanksysteme II: Implementation of Database Systems
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1657
14
1415
52
1309
25
1257
29
1229
24
iOS 18 adds a new 'Recovered' album function to retrieve lost or damaged photos
Jul 18, 2024 am 05:48 AM
Apple's latest releases of iOS18, iPadOS18 and macOS Sequoia systems have added an important feature to the Photos application, designed to help users easily recover photos and videos lost or damaged due to various reasons. The new feature introduces an album called "Recovered" in the Tools section of the Photos app that will automatically appear when a user has pictures or videos on their device that are not part of their photo library. The emergence of the "Recovered" album provides a solution for photos and videos lost due to database corruption, the camera application not saving to the photo library correctly, or a third-party application managing the photo library. Users only need a few simple steps
How does Hibernate implement polymorphic mapping?
Apr 17, 2024 pm 12:09 PM
Hibernate polymorphic mapping can map inherited classes to the database and provides the following mapping types: joined-subclass: Create a separate table for the subclass, including all columns of the parent class. table-per-class: Create a separate table for subclasses, containing only subclass-specific columns. union-subclass: similar to joined-subclass, but the parent class table unions all subclass columns.
Detailed tutorial on establishing a database connection using MySQLi in PHP
Jun 04, 2024 pm 01:42 PM
How to use MySQLi to establish a database connection in PHP: Include MySQLi extension (require_once) Create connection function (functionconnect_to_db) Call connection function ($conn=connect_to_db()) Execute query ($result=$conn->query()) Close connection ( $conn->close())
How to handle database connection errors in PHP
Jun 05, 2024 pm 02:16 PM
To handle database connection errors in PHP, you can use the following steps: Use mysqli_connect_errno() to obtain the error code. Use mysqli_connect_error() to get the error message. By capturing and logging these error messages, database connection issues can be easily identified and resolved, ensuring the smooth running of your application.
How to use database callback functions in Golang?
Jun 03, 2024 pm 02:20 PM
Using the database callback function in Golang can achieve: executing custom code after the specified database operation is completed. Add custom behavior through separate functions without writing additional code. Callback functions are available for insert, update, delete, and query operations. You must use the sql.Exec, sql.QueryRow, or sql.Query function to use the callback function.
How to connect to remote database using Golang?
Jun 01, 2024 pm 08:31 PM
Through the Go standard library database/sql package, you can connect to remote databases such as MySQL, PostgreSQL or SQLite: create a connection string containing database connection information. Use the sql.Open() function to open a database connection. Perform database operations such as SQL queries and insert operations. Use defer to close the database connection to release resources.
How to save JSON data to database in Golang?
Jun 06, 2024 am 11:24 AM
JSON data can be saved into a MySQL database by using the gjson library or the json.Unmarshal function. The gjson library provides convenience methods to parse JSON fields, and the json.Unmarshal function requires a target type pointer to unmarshal JSON data. Both methods require preparing SQL statements and performing insert operations to persist the data into the database.
How to handle database connections and operations using C++?
Jun 01, 2024 pm 07:24 PM
Use the DataAccessObjects (DAO) library in C++ to connect and operate the database, including establishing database connections, executing SQL queries, inserting new records and updating existing records. The specific steps are: 1. Include necessary library statements; 2. Open the database file; 3. Create a Recordset object to execute SQL queries or manipulate data; 4. Traverse the results or update records according to specific needs.
