数据库-----catalog与schema简介
在SQL环境下Catalog和Schema都属于抽象概念，主要用来解决命名冲突问题 一个数据库系统包含多个Catalog，每个Catalog包含多个Schema，每个Schema包含多个数据库对象（表、视图、字段等） 如数据库对象表的全限定名可表示为：Catalog名.Schema名.表名 ＳＱＬ
在SQL环境下Catalog和Schema都属于抽象概念，主要用来解决命名冲突问题
一个数据库系统包含多个Catalog，每个Catalog包含多个Schema，每个Schema包含多个数据库对象（表、视图、字段等）
如数据库对象表的全限定名可表示为：Catalog名.Schema名.表名
ＳＱＬ标准并不要求每个数据库对象的完全限定名称是唯一的，就象域名一样，如果喜欢的话，每个ＩＰ地址都可以拥有多个域名
从实现的角度来看，各种数据库系统对Catalog和Schema的支持和实现方式千差万别，比较简单而常用的实现方式是使用数据库名作为Catalog名，使用用户名作为Schema名，具体可参见下表：
|
供应商 |
Catalog支持 |
Schema支持 |
|
Oracle |
不支持 |
Oracle User ID |
|
MySQL |
不支持 |
数据库名 |
|
MS SQL Server |
数据库名 |
对象属主名，2005版开始有变 |
|
DB2 |
指定数据库对象时，Catalog部分省略 |
Catalog属主名 |
|
Sybase |
数据库名 |
数据库属主名 |
|
Informix |
不支持 |
不需要 |
|
PointBase |
不支持 |
数据库名 |
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