Oracle基础

* database
  A database is a set of files, located on disk, that store data. These files can exist independently of a database instance.
* database instance (对应mysql的database)
  An instance is a set of memory structures that manage database files. The instance consists of a shared memory area, called the system global area (SGA), and a set of background processes. An instance can exist independently of database files.
    sid： INSTANCE_NAME
    service name: SERVICE_NAMES，对外公布的名称，为网络监听服务
    sid用于实例区分各个数据库，service name用于外部链接
* user
  one user has one schema
  Each client process is associated with its own server process. The server process has its own private session memory, known as the program global area (PGA).

* schema
database metadata
schema is a collection of logical data structures, or schema objects(tables, indexes, views...)
可以理解为一个数据库名

start oracle:
su - oracle (login shell)
sqlplus / as sysdba
startup;