首先cmd - sqlplusw 普通用户登陆:用户名:scott(普通用户名) 密码:tiger(普通用户密码) 管理员登陆:用户名:system
首先cmd - sqlplusw
普通用户登陆:用户名:scott(普通用户名) 密码:tiger(普通用户密码)
管理员登陆:用户名:system 密码:system(管理员密码)
超级管理员登陆的时候注意:用户名:sys 密码:sys as sysdba(sys 为密码)
一、忘记除SYS、SYSTEM用户之外的用户的登录密码。
使用如下语句修改用户的密码。
ALTER USER user_name IDENTIFIED BY newpass;
注意:密码不能全是数字。并且不能是数字开头。否则会出现:ORA-00988: 口令缺失或无效
二、忘记SYS用户,或者是SYSTEM用户的密码。
如果是忘记SYSTEM用户的密码,可以用SYS用户登录。然后用ALTER USER 密令
修改密码。
ALTER USER SYSTEM IDENTIFIED BY newpass;
如果是忘记SYS用户的密码,可以用SYSTEM用户登录。然后用ALTER USER 密令
修改密码。
ALTER USER SYSTEM IDENTIFIED BY newpass;
三、如果SYS,SYSTEM用户的密码都忘记或是丢失。
这一项尤其重要。
可以使用ORAPWD.EXE 工具修改密码。
开始菜单->运行->输入‘CMD’,打开命令提示符窗口,,输入如下命令:
orapwd file=D:\Oracle\product\10.2.0\db_1\database\pwdctcsys.ora
password=newpass
这个命令重新生成了数据库的密码文件。密码文件的位置在ORACLE_HOME目录下
的\database目录下。
这个密码是修改sys用户的密码。除sys和system其他用户的密码不会改变。
四、查看Oracle系统里的用户列表
select * from all_users;

MySQL 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.

MySQL 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.

MySQL 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.

InnoDB'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.

The main reasons for poor MySQL query performance include not using indexes, wrong execution plan selection by the query optimizer, unreasonable table design, excessive data volume and lock competition. 1. No index causes slow querying, and adding indexes can significantly improve performance. 2. Use the EXPLAIN command to analyze the query plan and find out the optimizer error. 3. Reconstructing the table structure and optimizing JOIN conditions can improve table design problems. 4. When the data volume is large, partitioning and table division strategies are adopted. 5. In a high concurrency environment, optimizing transactions and locking strategies can reduce lock competition.

In database optimization, indexing strategies should be selected according to query requirements: 1. When the query involves multiple columns and the order of conditions is fixed, use composite indexes; 2. When the query involves multiple columns but the order of conditions is not fixed, use multiple single-column indexes. Composite indexes are suitable for optimizing multi-column queries, while single-column indexes are suitable for single-column queries.

To optimize MySQL slow query, slowquerylog and performance_schema need to be used: 1. Enable slowquerylog and set thresholds to record slow query; 2. Use performance_schema to analyze query execution details, find out performance bottlenecks and optimize.

MySQL and SQL are essential skills for developers. 1.MySQL is an open source relational database management system, and SQL is the standard language used to manage and operate databases. 2.MySQL supports multiple storage engines through efficient data storage and retrieval functions, and SQL completes complex data operations through simple statements. 3. Examples of usage include basic queries and advanced queries, such as filtering and sorting by condition. 4. Common errors include syntax errors and performance issues, which can be optimized by checking SQL statements and using EXPLAIN commands. 5. Performance optimization techniques include using indexes, avoiding full table scanning, optimizing JOIN operations and improving code readability.


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