对于一台Oracle服务器下，安装了多个实例，当执行sqlplus / as sysdba时，连接的是哪个实例呢？其实，当执行sqlplus / as sysdba
对于一台Oracle服务器下，，安装了多个实例，当执行sqlplus / as sysdba时，连接的是哪个实例呢？
其实，当执行sqlplus / as sysdba时,此时用户名和密码是可以随便输入的,也可以如现在这样为空，不输入。本质上在于此时验证的根本不是密码文件，而是通过操作系统进来的，这时候连接的数据库的SID由操作系统环境变量$ORACLE_SID决定,查看方式为echo V$ORACLE_SID.此SID的验证，可以在sqlplus / as sysdba进去后，执行数据库命令查看:select t.instance_name from v$instance t.
对于此SID对应的数据库的更详细的环境信息, 可以在$ORACLE_HOME/network/admin/tnsnames.ora里进行查看。
当Oracle数据库的sys用户密码忘记的时候，可以通过操作系方式:sqlplus / as sysdba进入数据库,然后执行alter user sys identified by xxx来修改sys用户密码。
对于执行sqlplus / as sysdba，要求操作用户在DBA用户组，如oracle用户可以执行此命令，而其他普通用户执行此命令时，会报权限不足的错误。
对于$ORACLE_SID值的修改,bash shell模式下,在.bash_profile文件里,加上export ORACLE_SID=xxx,然后使得修改生效:source .bash_profile即可。这样sqlplus / as sysdba,连接的就是.bash_profile文件里配置的$ORACLE_SID的值。
相关阅读：
rlwrap - 解决Linux下SQLPLUS退格、上翻键乱码问题
SQLPLUS spool 到动态日志文件名
Oracle SQLPLUS提示符设置
通过设置SQLPLUS ARRAYSIZE(行预取)加快SQL返回速度
MySQL's Place: Databases and ProgrammingApr 13, 2025 am 12:18 AMMySQL's position in databases and programming is very important. It is an open source relational database management system that is widely used in various application scenarios. 1) MySQL provides efficient data storage, organization and retrieval functions, supporting Web, mobile and enterprise-level systems. 2) It uses a client-server architecture, supports multiple storage engines and index optimization. 3) Basic usages include creating tables and inserting data, and advanced usages involve multi-table JOINs and complex queries. 4) Frequently asked questions such as SQL syntax errors and performance issues can be debugged through the EXPLAIN command and slow query log. 5) Performance optimization methods include rational use of indexes, optimized query and use of caches. Best practices include using transactions and PreparedStatemen
MySQL: From Small Businesses to Large EnterprisesApr 13, 2025 am 12:17 AMMySQL is suitable for small and large enterprises. 1) Small businesses can use MySQL for basic data management, such as storing customer information. 2) Large enterprises can use MySQL to process massive data and complex business logic to optimize query performance and transaction processing.
What are phantom reads and how does InnoDB prevent them (Next-Key Locking)?Apr 13, 2025 am 12:16 AMInnoDB effectively prevents phantom reading through Next-KeyLocking mechanism. 1) Next-KeyLocking combines row lock and gap lock to lock records and their gaps to prevent new records from being inserted. 2) In practical applications, by optimizing query and adjusting isolation levels, lock competition can be reduced and concurrency performance can be improved.
MySQL: Not a Programming Language, But...Apr 13, 2025 am 12:03 AMMySQL is not a programming language, but its query language SQL has the characteristics of a programming language: 1. SQL supports conditional judgment, loops and variable operations; 2. Through stored procedures, triggers and functions, users can perform complex logical operations in the database.
MySQL: An Introduction to the World's Most Popular DatabaseApr 12, 2025 am 12:18 AMMySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.
The Importance of MySQL: Data Storage and ManagementApr 12, 2025 am 12:18 AMMySQL is an open source relational database management system suitable for data storage, management, query and security. 1. It supports a variety of operating systems and is widely used in Web applications and other fields. 2. Through the client-server architecture and different storage engines, MySQL processes data efficiently. 3. Basic usage includes creating databases and tables, inserting, querying and updating data. 4. Advanced usage involves complex queries and stored procedures. 5. Common errors can be debugged through the EXPLAIN statement. 6. Performance optimization includes the rational use of indexes and optimized query statements.
Why Use MySQL? Benefits and AdvantagesApr 12, 2025 am 12:17 AMMySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.
Describe InnoDB locking mechanisms (shared locks, exclusive locks, intention locks, record locks, gap locks, next-key locks).Apr 12, 2025 am 12:16 AMInnoDB's lock mechanisms include shared locks, exclusive locks, intention locks, record locks, gap locks and next key locks. 1. Shared lock allows transactions to read data without preventing other transactions from reading. 2. Exclusive lock prevents other transactions from reading and modifying data. 3. Intention lock optimizes lock efficiency. 4. Record lock lock index record. 5. Gap lock locks index recording gap. 6. The next key lock is a combination of record lock and gap lock to ensure data consistency.
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
AI Hentai Generator
Generate AI Hentai for free.
Hot Article
Hot Tools
MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.
DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software
EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function
SublimeText3 Linux new version
SublimeText3 Linux latest version
SublimeText3 Chinese version
Chinese version, very easy to use
