Advanced Database Management System - Tutorials and Notes: Codd's Twelve Rules - Rule 3 - Systematic treatment of NULL values

Thursday, 19 February 2015

Codd's Twelve Rules - Rule 3 - Systematic treatment of NULL values


Codd's Twelve Rules - Rule 3 - Systematic treatment of NULL values



Rule 3
Systematic treatment of NULL values
Rule
NULL values (distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational RDBMS for representing missing information in a systematic way, independent of data type.
Description
This rule demands that we must be able to use a NULL placeholder irrespective of data type used. NULLs are distinct from an empty character string or any other number, and they are always to be considered as unknown values. This rule insists provisions for manipulating NULL values in all the possible ways.
Example
SELECT Emp_Salary FROM Employee WHERE EPhone IS NULL;
          This query should return Emp_Salary if EPhone value is NULL/Not known.
Some DBMS that fulfills this property
Oracle, SQL Server, and MySQL supports NULL values to be handled. They provide mechanisms to handle NULL values like other values.


No comments:

Post a comment

Featured Content

Multiple choice questions in Natural Language Processing Home

MCQ in Natural Language Processing, Quiz questions with answers in NLP, Top interview questions in NLP with answers Multiple Choice Que...

All time most popular contents