Class XII Informatics Practices Paper (Chapter Wise With Answer)

ORACLE SQL REVISION TOUR AND DATABASE FUNDAMENTALS

Q1. (a)Define the term candidate key and foreign key with respect to database.
(b) Define the term primary key and alternate key with respect to database.

Ans. (a) CANDIDATE KEY- All attribute combinations inside a relation that can serve as a primary key are candidate keys as they are candidates for primary key position.
FOREIGN KEY- A non-key attribute, whose values are derived from the primary key of some other table, is known as foreign key in its current table.
(b)PRIMARY KEY- This refers to a set of one or more attributes that can uniquely identify tuples within the relation.
ALTERNATE KEY- A candidate key, that is not primary key, is called an alternate key.

Q2. Differentiate between DDL and DML commands. Give one example of each type of command.
Ans: The Data Definition Language (DDL) commands, as the name suggests, allow you to perform tasks related to data definition. That is, through these commands, you can perform tasks alter and drop schema objects, grant and revoke privileges etc.
The Data Manipulation Language (DML) commands, as the name suggests, are used to manipulate data. That is, DML commands query and manipulate data in existing schema objects.

Q3. Name the keyword used to (i) assign a value as no data (ii) avoid duplicate rows in SQL query.
Ans: (I) NULL (ii) UNIQUE

Q4. What is a view? Why does view not requires any physical storage?
Ans. A view is a virtual table that can be thought of as an SQL SELECT statement that selects data from a single table or joined table(s), but can be accessed as though it were a single table.
A view does not require physical storage because a view is a virtual table that does not exist in reality, but is a logical definition of a set of relative columns, usually from multiple tables.

Q5. Define SQL. Name the different SQL subcategories.
Ans: The Structure Query Language (SQL) is a language that enables you to create and operate on relational databases. It is a standard relational database language.SQL command is divided into following categories:
(i) Data Definition Language (DDL) Commands
(ii)Data Manipulation Language (DML) Commands
(iii) Transaction Control Language (TCL) Commands
(iv) Session Control Commands
(vi)System Control Commands

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