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Creating views with check option: This option limits those updates of data values that cause records to go off the view. The following instance tells this in more detail:
Example: To produce a view for employees of Department = 30, such that user cannot alter the department number from the view:
CREATE OR REPLACE VIEW EMPD30 AS
SELECT EMPNO EMPL_NUM, ENAME NAME, SAL SALARY FROM EMP
WHERE DEPTNO=30
WITH CHECK OPTION;
Now the user cannot alter the department number of any record of view EMPD30. If this change is permitted then the record in which the change has been made will go off the view as the view is only for department-30. This restricted due to use of WITH CHECK OPTION clause
Explain outer join? Outer Join - If there are any values in one table which do not have corresponding value(s) in the other, in an equi-join which will not be chosen. Such ro
Attribute Preservation This is a easy and obvious necessity that includes preserving all the attributes that were there in the relation that is being decomposed.
How nulls are treated in comparison operator? Along with comparison (relational) operators, the null values are ignored as we cannot derive the relation along with the given op
What is inheritance? Define it in detail? Inheritance Inheritance can be at the levels of types, or at the level of tables we first consider inheritance of types, then i
Determine the Persistent object Persistent object can be stored in one of the following: Files Cheap, permanent, simple storage Low level (Write, Read) Ap
Insertion Anomaly: Inability to show certain information-The primary key of the over relation be (enrolment number, Cno). Any new tuple to be inserted in the relation should have
Illustrate the statement 'Projection operation distributes over the union operation'. Give an example. Ans: Π L (E 1 ∪ E 2 ) = (Π L (E 1 )) ∪ (Π L (E 2 )) This says th
What is the full form of ODBC ? ODBC stands for Open Database Connectivity.
How does a query tree represent a relational algebra expression? Discuss any three rules for query optimisation, giving example as to when should each rule be applied. Ans
First Normal Form and second normal form First Normal Form (1NF) A relation is said to be in 1NF if it having no non-atomic values and each row can give a unique combinat
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