如何在 Oracle数据库里写出高质量的SQL语句,如何在Oracle数据库里对有性能问题的SQL做诊断和调整,这是DBA们在ORACLE数据库实践
如何在 Oracle数据库里写出高质量的SQL语句,如何在Oracle数据库里对有性能问题的SQL做诊断和调整,这是DBA们在ORACLE数据库实践中不可避免的难题。下面就让我们来分析一下拿到一条问题sql后我们可以如何去开始我们的优化思路。
对于有问题的SQL做SQL优化的具体步骤一般为:
1、查看该SQL语句的执行计划,并结合其资源消耗情况和相关统计信息、Trace文件来分析其执行计划是否合理;
2、通过修正措施(如调整该SQL的执行计划等)来对该SQL做调整以缩短其执行时间,Oracle数据库里SQL优化的终极目标就是要缩短目标SQL语句的执行时间。要达到上述目的,我们通常只有如下三种方法可以选择:
1、降低目标SQL语句的资源消耗;
2、并行执行目标SQL语句;
3、平衡系统的资源消耗。
方法1:降低目标SQL语句的资源消耗”以缩短执行时间,这是最常用的SQL优化方法。这种方法的核心是要么通过在不更改业务逻辑的情况下改写SQL来降低目标SQL语句的资源消耗,要么不改SQL但通过调整执行计划或相关表的数据来降低目标SQL语句的资源消耗。
方法2:并行执行目标SQL语句”,这实际上是以额外的资源消耗来换取执行时间的缩短,很多情况下使用并行是针对某些SQL的唯一优化手段。
方法3:平衡系统的资源消耗” 可以避免不必要的资源争用所导致的目标SQL语句执行时间的增长。对某些SQL而言,其执行时间的增长或者不稳定(时快时慢)不是由于其执行计划的问题,,而是由于在目标SQL执行时系统处于高负荷状态,执行目标SQL所需要的硬件资源(CPU、内存、IO等)得不到保障,存在争用的情况。在这样的情况下,如果我们能平衡系统的资源消耗,把一些跟目标SQL同时执行的不重要但很消耗系统资源的操作(如报表、批处理等)挪到系统不忙的时候执行,比如把它们挪到晚上执行,那么就可以释放部分系统硬件资源以确保目标SQL执行时所需要的硬件资源不再存在争用的情况,进而就避免了其执行时间的增长或者不稳定。

InnoDBBufferPool reduces disk I/O by caching data and indexing pages, improving database performance. Its working principle includes: 1. Data reading: Read data from BufferPool; 2. Data writing: After modifying the data, write to BufferPool and refresh it to disk regularly; 3. Cache management: Use the LRU algorithm to manage cache pages; 4. Reading mechanism: Load adjacent data pages in advance. By sizing the BufferPool and using multiple instances, database performance can be optimized.

Compared with other programming languages, MySQL is mainly used to store and manage data, while other languages such as Python, Java, and C are used for logical processing and application development. MySQL is known for its high performance, scalability and cross-platform support, suitable for data management needs, while other languages have advantages in their respective fields such as data analytics, enterprise applications, and system programming.

MySQL is worth learning because it is a powerful open source database management system suitable for data storage, management and analysis. 1) MySQL is a relational database that uses SQL to operate data and is suitable for structured data management. 2) The SQL language is the key to interacting with MySQL and supports CRUD operations. 3) The working principle of MySQL includes client/server architecture, storage engine and query optimizer. 4) Basic usage includes creating databases and tables, and advanced usage involves joining tables using JOIN. 5) Common errors include syntax errors and permission issues, and debugging skills include checking syntax and using EXPLAIN commands. 6) Performance optimization involves the use of indexes, optimization of SQL statements and regular maintenance of databases.

MySQL is suitable for beginners to learn database skills. 1. Install MySQL server and client tools. 2. Understand basic SQL queries, such as SELECT. 3. Master data operations: create tables, insert, update, and delete data. 4. Learn advanced skills: subquery and window functions. 5. Debugging and optimization: Check syntax, use indexes, avoid SELECT*, and use LIMIT.

MySQL efficiently manages structured data through table structure and SQL query, and implements inter-table relationships through foreign keys. 1. Define the data format and type when creating a table. 2. Use foreign keys to establish relationships between tables. 3. Improve performance through indexing and query optimization. 4. Regularly backup and monitor databases to ensure data security and performance optimization.

MySQL is an open source relational database management system that is widely used in Web development. Its key features include: 1. Supports multiple storage engines, such as InnoDB and MyISAM, suitable for different scenarios; 2. Provides master-slave replication functions to facilitate load balancing and data backup; 3. Improve query efficiency through query optimization and index use.

SQL is used to interact with MySQL database to realize data addition, deletion, modification, inspection and database design. 1) SQL performs data operations through SELECT, INSERT, UPDATE, DELETE statements; 2) Use CREATE, ALTER, DROP statements for database design and management; 3) Complex queries and data analysis are implemented through SQL to improve business decision-making efficiency.

The basic operations of MySQL include creating databases, tables, and using SQL to perform CRUD operations on data. 1. Create a database: CREATEDATABASEmy_first_db; 2. Create a table: CREATETABLEbooks(idINTAUTO_INCREMENTPRIMARYKEY, titleVARCHAR(100)NOTNULL, authorVARCHAR(100)NOTNULL, published_yearINT); 3. Insert data: INSERTINTObooks(title, author, published_year)VA


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