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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.
Explain Hierarchical Model ? Hierarchical Model - It was established to model several kinds of hierarchical organizations which exist in the real world. It uses tree structur
What is meant by computing the closure of a set of functional dependency? The closure of F denoted by F + is the set of functional dependencies logically implied by F.
Explain the Deferred Update The deferred update methods do not physically update the database on disk till after a transaction reaches its commit point; after that the updates
Question 1 List and explain various Normal Forms. How BCNF differs from the Third Normal Form and 4th Normal forms? Question 2 Describe the concepts of Structural Semantic Da
Determine the language that needs a user to specify the data to be retrieved with no specifying exactly how to get it is Ans: Non-Procedural DML
a. Construct a query around any one of the functional divisions you made in 4a such that if executed in the distributed design of 4 would require reconstruction of at least two ho
how to implement hyrise in C plus plus
Example : Search the name, department number and salary of employees drawing minimum salary in that department. SELECT ENAME, SAL, DEPTNO FROM EMP WHERE SAL IN (SELECT MI
What is the used of specifying alias? Specifying alias: is used to rename column or attribute in a table.
I need help in doing my dbms project
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