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Define entity integrity and referential integrity. How does SQL allow specification of these?
Ans: Entity Integrity Rule- If the attribute A of relation R is a prime attribute of R after that A cannot accept null values.
Referential Integrity Rule- In referential integrity, it is made sure that a value that appears in one relation for a given set of attributes as well appears for a particular set of attributes in another relation.
In SQL, referential integrity and entity integrity rules are implemented as constraints on the relation known as reference Key constraint and primary Key constraint correspondingly.
These constraints can be fixed with relation at the time of creation of the relations or after the creation of the relations by altering the definition of the relations. For instance:
What is disadvantage of multiple inheritances? There is potential ambiguity if the similar variable or method can be inherited from more than one superclass.eg: student class m
explain the mapping constraints
what are the purposes of dbms in details
It can be easily defined as: The database must not have any unmatched foreign key values. The term "unmatched foreign key value" means a foreign key value for which there doe
What is Disadvantages Of DBMS ? 1. Cost of Software and Hardware and Migration - A important disadvantage of the DBMS system is cost. 2. Reduced Response and Throughpu
The issues relating to the Design of the Physical Database Files Physical File is a file as stored on the disk. The major issues relating to physical files are: • Cons
Operator Precedence The basic operators used in SQL are * / - + Operators of the similar priority are evaluated From Left to right Parentheses are used to force priorit
Explain the concept of QBE? Query-by-example represents a visual/graphical approach for accessing information in a database by the use of query templates called as skeleton tab
A constraint named less_than_20 was defined on the field date_of_birth of table student. Delete this constraint. ALTER TABLE student DROP CONSTRAINT less_than_20;
Whenever the LIMIT clause will be used? LIMIT is used for the following kinds of problems: 1) Answering questions about first or last and largest or smallest 2) Splitting
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