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Explain entity integrity and referential integrity rules within relational model. Show how these are realized in SQL?
Entity Integrity Rule - No primary key value could be null.
Referential Integrity Rule - In referential integrity, it is ensured in which a value which appears in one relation for a given set of attributes also appears for a certain set of attributes within another relation.
In SQL, entity integrity and referential integrity rules are implemented as constraints on the relation known as primary key constraint or reference key constraint corresponding. These constraints can be specified along with relation at the time of creation of the relations or after the creation of the relations through altering the definition of the relations. For instance:
CREATE TABLE DEPT
(DEPTNO NUMBER PRIMARY KEY,
DNAME VARCHAR2(15));
CREATE TABLE EMP
(EMPNO NUMBER PRIMARY KEY,
20
ENAME VARCHAR2(15),
JOB VARCHAR2(10),
DEPTNO NUMBER REFERENCES DEPT(DEPTNO));
Australian Bureau of Statistics (ABS) provides retail data for different groups and different states as well as the aggregate numbers. Table 11 " Retail Turnover, State by Industry
How many levels can be viewed in Architecture of the database ? Architecture of the database can be viewed as three levels.
What is horizontal fragmentation? Horizontal fragmentation divides the relation by assuming every tuple of r to one or more fragments
difference between internal schema and external schema in DBMS
Create an entity relationship diagram, Database Management System
Why does a DBMS query language is designed? A DBMS query language is designed to support end users who use English-like commands. support in the development of complex applicat
Why, generally does an object-oriented system use the relational DBMS? The reasons for using relational DBMS for OO systems could be any combination of following: a. Many or
what is union compatable?
Which operations need the participating relations to be union compatible? A UNION, INTERSECTION and DIFFERENCE operations need the participating relations to be union compatibl
Before we talk about the relational model in more detail, let us first define some very basic terms used in this model. Tuple Every row in a table shows a record and is cal
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