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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 inheritance at the level of labels.
Type inheritance
Assume that we have the following type definition for people
create type person
(name varchar(20)
address varchar(20))
Table inheritance
Create table people of person
The consistency requirements for sub tables are
1. Each tuple of the sub table can correspond to at most single tuple in each of its immediate sub tables.
2. SQL:1999 has an additional constraint that all the tuples corresponding to each other must be derived from single tuple .
Why 'AS' clause is used in SQL ? 'As' clause is used for Rename operation. ‘AS' clause is used in SQL for rename operation. (e.g., SELECT ENO AS EMPLOYEE_NO FROM EMP)
Which operation is used if we are interested in only certain columns of a table? PROJECTION operation is used if we are interested in only certain columns of a table.
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The result of the UNION operation between R1 and R2 is a relation that includes? The result of the operation between R1 and R2 includes all the tuples of R1 and R2 which have c
List any two disadvantages of a database system ? The disadvantages of database system are: • Database systems are difficult, complex, and time-consuming to design. • Substanti
What is the disadvantage of a call by reference? During a call by reference damage or loss of data is not restricted to the subroutine, but will instantly lead to alters to th
An Enterprising group of Entrepreneurs introduced a new business named StoreItRite which is based on data storage and retrieval services. It provides the services and the company c
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