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Before defines the second type of integrity constraint, viz., Entity Integrity, we should be well-known with the concept of NULL.
Mostly, NULL is intended as a basis for dealing with the trouble of missing information. This type of situation is frequently encountered in the actual world. For instance, historical records sometimes have entries such as "Date of birth unknown", or police records may contain the entry "Present whereabouts unknown." Therefore it is necessary to have some way of dealing with such concepts in database systems.
Therefore Codd proposed an approach to this issue that creates use of special markers known as NULL to show such missing information.
A given attribute in the relation may or may not be allowed to include NULL. However, can the Primary key or any of its components (in case of the primary key is a composite key) contain a NULL? To answer this Query an Entity Integrity Rule states: No component of the primary key of a relation is permitted to accept NULL. In different words, the definition of each attribute involved in the primary key of any basic relation have to explicitly or implicitly contain the specifications of NULL NOT ALLOWED.
What is a view in SQL? When can views be updated? A view is a virtual table which consists of columns from one or more tables. Through it is same to a table; it is stored in
Law Associates is a large legal practice based in Sydney. You have been asked to design a data model for the practice based upon the following specification: The practice emplo
Describe an data dictionary? A data dictionary is a data structure which keeps meta data about the structure of the database ie. the schema of the database.
Submit SQL SELECT Statements to demonstrate several reports off your database, according to the following guidelines: You must submit at least 5 SELECT Statements. Each
System R was developed and designed over a period of 1974-79 at IBM San Jose Research Company. Its purpose was to illustrate that it is possible to create a Relational System tha
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Set Difference If R1 and R2 are two union compatible relations or relations then result of R3 =R1- R2 is the relation that have only those tuples that are in R1 but not in R2.
It defines that no primary key value can be null. This is as the primary key is used to recognize individual tuple in the relation. So we will not be able to recognize the records
i need help with creating database system for a library
distributed quey processing
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