States of Integrity Constraints As part of constraint definition, you can specify how and when Oracle Database should enforce the constraint, thereby determining the constraint state. Checks for Modified and Existing Data The database enables you to…

oreign key constraints (also known as referential constraints or referential integrity constraints) enable you to define required relationships between and within tables. For example, a typical foreign key constraint might state that every employee i…

An informational constraint is a constraint attribute that can be used by the SQL compiler to improve the access to data. Informational constraints are not enforced by the database manager, and are not used for additional verification of data; rather…

from Database Design to Physical Form CREATE TABLE integrity constraints (完整性约束) CREATE VIEW Security The GRANT & REVOKE statements Catalogs Schemas Introduction ->The DBA(数据库管理员) must begin by creating the tables and constraints(约束) and loading th…

原文地址:http://i.cnblogs.com/EditPosts.aspx?opt=1. I wrote a first version of this posting on consistency models about a year ago, but I was never happy with it as it was written in haste and the topic is important enough to receive a more thorough trea…

应该说搞分布式系统必读的文章了,转过来,这是2008年12月Werner revise过的版本,先贴上内容简介:分布式系统的CAP理论 CAP理论(data consistency, system availability, and tolerance),也就是数据一致性,系统可用性和网络分区容错性,在一个分布式系统中CAP是不能同时保证的,最多只能同时满足两个.如果一个系统不必考虑网络分区容错性,那么它可以同时取得数据一致性和可用性,这通常可以通过处理协议来保证.    然而不考虑网络分区容错…

http://exploredegrees.stanford.edu/coursedescriptions/cs/ CS 101. Introduction to Computing Principles. 3-5 Units. Introduces the essential ideas of computing: data representation, algorithms, programming "code", computer hardware, networking, s…

环境: 服务端:RHEL6.4 + Oracle 11.2.0.4 目录: 一. 创建外部表 1.1 创建外部表需要的目录 1.2 创建外部表 1.3 创建外部表源文件 1.4 查询外部表 二. 加载外部表数据到普通表 2.1 创建普通表 2.2 直接插入 2.3 直接路径插入 三.References 一. 创建外部表 1.1 创建外部表需要的目录 create or replace directory admin as '/u01/jingyu'; 1.2 创建外部表 drop table…

不同于SQL Server中NULL表示值是未知的(Unknown Value),没有数据类型,但是,在SSIS中,NULL是有数据类型的,要获取某一个NULL值,必须指定数据类型,例如,变量 Int32的“NULL值”是 NULL(DT_I4),默认值是0.对于变量和参数,不允许有NULL值,因此,NULL值是指默认值,如果变量或参数的值未被显式设置时,SSIS使用默认值.对于Data Flow组件,SSIS保持源数据的NULL值. 一,Variable和Parameter的默认值 在SSIS…

ORACLE基本数据类型(亦叫内置数据类型 built-in datatypes)可以按类型分为:字符串类型.数字类型.日期类型.LOB类型.LONG RAW& RAW类型.ROWID & UROWID类型. 在讲叙字符串类型前,先要讲一下编码.字符串类型的数据可依编码方式分成数据库字符集(CHAR/VARCHAR2/CLOB/LONG)和国际字符集(NCHAR/NVARCHAR2/NCLOB)两种.数据库中的字符串数据都通过字符集将字符转换为数字后(二进制),才存储到数据块中.通过不同的…