查看Oracle数据库状态
查看Oracle数据库状态 无 show sgaset wrap offset linesize 400-- 查看正在运行的后台进程select * from v$bgprocess;select * from v$bgprocess where paddr'00';--查看数据库的物理组成:文件情况select * from v$controlfile;select * from v$datafile;se
查看Oracle数据库状态show sga set wrap off set linesize 400 -- 查看正在运行的后台进程 select * from v$bgprocess; select * from v$bgprocess where paddr<>'00'; --查看数据库的物理组成:文件情况 select * from v$controlfile; select * from v$datafile; select * from v$logfile; --查看实例内存情况 show parameter sga show parameter shared show parameter db_cache show parameter log alter system set db_cache_size=64m; //可以动态修改sga中内存区的大小,但是不能超过sga的最大内存 select * from dept; --表空间管理 CREATE TABLESPACE tbs2 DATAFILE 'D:\oracle\oradata\APTECH\tbs2_01.dbf' SIZE 50M; conn sys/admin as sysdba(重启数据库必须以sys用户登陆) shutdown immediate(关闭数据库) 启动数据库的三个步骤: startup nomount (启动实例) alter database mount;(装载数据库,读取控制文件) alter database open;(打开数据库,对数据文件,日志文件进行一致性校验) --用户管理 -- Create the user CREATE USER MARTIN IDENTIFIED BY martinpwd DEFAULT TABLESPACE USERS TEMPORARY TABLESPACE TEMP; -- Grant role privileges GRANT CONNECT TO MARTIN; GRANT RESOURCE TO MARTIN; -- 如果不使用 CONNECT 角色,则需要逐个赋予用户权限 GRANT CREATE SESSION TO MARTIN; GRANT CREATE TABLE TO MARTIN; GRANT CREATE VIEW TO MARTIN; GRANT CREATE SEQUENCE TO MARTIN; GRANT CREATE SEQUENCE TO MARTIN; GRANT SELECT ON TEST TO MARTIN; GRANT ALL ON TEST TO MARTIN; -- 授予用户使用表空间 USERS 的权限 ALTER USER MARTIN QUOTA UNLIMITED ON USERS; --修改用户密码 ALTER USER MARTIN IDENTIFIED BY martinpass; --修改自己的密码 在sql*plus中直接输入password命令即可 --删除用户 DROP USER MARTIN CASCADE; -- 查看用户 MARTIN 的信息 select USERNAME,USER_ID,DEFAULT_TABLESPACE,TEMPORARY_TABLESPACE from dba_users where username = 'MARTIN';

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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.

Solutions to Oracle cannot be opened include: 1. Start the database service; 2. Start the listener; 3. Check port conflicts; 4. Set environment variables correctly; 5. Make sure the firewall or antivirus software does not block the connection; 6. Check whether the server is closed; 7. Use RMAN to recover corrupt files; 8. Check whether the TNS service name is correct; 9. Check network connection; 10. Reinstall Oracle software.

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.

The method to solve the Oracle cursor closure problem includes: explicitly closing the cursor using the CLOSE statement. Declare the cursor in the FOR UPDATE clause so that it automatically closes after the scope is ended. Declare the cursor in the USING clause so that it automatically closes when the associated PL/SQL variable is closed. Use exception handling to ensure that the cursor is closed in any exception situation. Use the connection pool to automatically close the cursor. Disable automatic submission and delay cursor closing.

In Oracle, the FOR LOOP loop can create cursors dynamically. The steps are: 1. Define the cursor type; 2. Create the loop; 3. Create the cursor dynamically; 4. Execute the cursor; 5. Close the cursor. Example: A cursor can be created cycle-by-circuit to display the names and salaries of the top 10 employees.

To stop an Oracle database, perform the following steps: 1. Connect to the database; 2. Shutdown immediately; 3. Shutdown abort completely.

Building a Hadoop Distributed File System (HDFS) on a CentOS system requires multiple steps. This article provides a brief configuration guide. 1. Prepare to install JDK in the early stage: Install JavaDevelopmentKit (JDK) on all nodes, and the version must be compatible with Hadoop. The installation package can be downloaded from the Oracle official website. Environment variable configuration: Edit /etc/profile file, set Java and Hadoop environment variables, so that the system can find the installation path of JDK and Hadoop. 2. Security configuration: SSH password-free login to generate SSH key: Use the ssh-keygen command on each node

SQL statements can be created and executed based on runtime input by using Oracle's dynamic SQL. The steps include: preparing an empty string variable to store dynamically generated SQL statements. Use the EXECUTE IMMEDIATE or PREPARE statement to compile and execute dynamic SQL statements. Use bind variable to pass user input or other dynamic values to dynamic SQL. Use EXECUTE IMMEDIATE or EXECUTE to execute dynamic SQL statements.
