Null (SQL)的封面
书籍主题:

Null (SQL)

SQL, Edgar F. Codd, Relational database management system

VolvPress (2013-08-13 )

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ISBN-13:

978-620-1-57509-7

ISBN-10:
620157509X
EAN:
9786201575097
书籍语言:
英文
作品简介:
Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Null is a special marker used in Structured Query Language to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL Null serves to fulfill the requirement that all true relational database management systems support a representation of "missing information and inapplicable information". Codd also introduced the use of the lowercase Greek omega symbol to represent Null in database theory. NULL is also an SQL reserved keyword used to identify the Null special marker. Null has been the focus of controversy and a source of debate because of its associated three-valued logic, special requirements for its use in SQL joins, and the special handling required by aggregate functions and SQL grouping operators. Although special functions and predicates are provided to properly handle Nulls, opponents feel that resolving these issues introduces unnecessary complexity and inconsistency into the relational model of databases.
出版社 :
VolvPress
网址:
http://www.betascript-publishing.com
出版发行由:
Sören Jehoiakim Ethan
页码 :
72
发表日期:
2013-08-13
现货:
备有现货
类别:
数据通讯,网络
价格:
29.00 €
关键词:
Management, language, Database, query, marker, Null

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