MCQ Test: Database Management System - 1 - JKSSB Patwari MCQ

Concept:

Superkey is a set of attributes within a table whose values can be used to uniquely identify a tuple. A candidate key is a minimal superkey.

Superkey is superset of candidate key or primary key.

Explanation:

Primary key is VY. (given)

All superkeys must contain this primary key VY. From the given keys, key, which doesn’t contain

the VY.

Here, option 2: VWXZ

“VWXZ” doesn’t contain the primary key VY. So, it is not a superkey.

Function Dependencies:

{(E, F} → {G}, {F} → {I, J}, {E, H} → {K, L}, {K} → {M}, {L} → {N}}

Option 1: {E, F}

{E, F}⁺ = {E, F, G, I, J}

Since K, L, M and N is missing in RHS ∴ it is not a key

Also, {E} cannot be a key because {E} is subset of {E, F}

Option 2: {E, F, H}

{E, F, H}⁺ = {E, F, H, G, I, J, K, L, M, N}

∴ it is a key

Key for R is {E, F, H}.

Important Points:

In relation algebra, key is primary key or candidate key.

{E, F, H, K, L} is super key. 

Concept:

Total participation: It specifies that each entity in the entity set must compulsorily participate in at least one relationship instance in that relationship set.

Partial participation: It specifies that each entity in the entity set may or may not participate in the relationship instance in that relationship set.

Explanation:

In one to many or many to one relation, the relation between two entities is merged on the many side with total participation. As, it is given that relationship R doesn’t have its own attributes. So, it must be combined with entity A. So, the relation must be many to one and there should be total participation of A in R.

Rules for finding a minimum number of tables required for an ER diagram:

1) A strong entity with single or composite attributes requires one table.

2) A strong entity with multivalued attributes requires two tables.

3) In the case of many to many relations between two entities, 3 tables are required.

Explanation:

There is one to many relationships between R₁and R₂. So, two tables are required for two entities. But, entity R₁ contains multivalued attribute B, due to which one table for this is also needed.

Here we have 1 to Many relation so we requires two tables.

Attribute B being multi-valued, we need to remove the multi-valued attribute B to convert the given entity-relationship diagram into a relational database.

As relational database do not allow multi-valued attributes. We have to introduce a new table.

So, the number of tables is as below:
R1
R12R2
A table for B (Multi-valued attribute)
So, a total of 3 tables are required for the given entity relational diagram.

So, option 3 is the correct answer.

Concept:

The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.

The ALTER TABLE statement is also used to add and drop various constraints on an existing table.

ADD Column

To add a column in a table, use the following syntax:

ALTER TABLE table_name ADD column_name datatype;

DROP COLUMN

To delete a column in a table, use the following syntax (notice that some database systems don't allow deleting a column):

ALTER TABLE table_name DROP COLUMN column_name;

To make manipulations in a column of a specific table, the "alter" command is used. To understand it more clearly, consider the following example:

The "COUNT" keyword is used to find the total number of values inside a column. So whenever a user wants to find the total values in a column, he can use the keyword "COUNT".

The database's external level is the one and only level that is considered the closest level to the end-users. So the correct answer will be the B.

The database management query language is generally designed by keeping in mind that it must support the end-users who are familiar with the English-like commands. It should also boost the process of development of the complex applications software and helps in specifying the structure of the database.

A database's architecture can be viewed as the three levels of abstraction that are named as the internal level, the external level, and the conceptual level. Therefore the correct answer is C.

The term "DML" refers to the data manipulation language, which is commonly used to perform basic operations such as insert data, delete, and update data in a database. So the correct answer will be B.

The term "SQL" stands for the structured query language, which is one of the most widely, used programming languages for relational databases. It can also be used for managing and organizing data in all sorts of systems in which different data relationships exist. Therefore the correct answer is C.

The Database management system can also considered as the set of programs that enables users to create and maintain the database.

The term "TCL" refers to the Transaction Control Language, which is another language just like the "DDL" and "DML". The commands like commit, save point, rollback come under the TCL used to control the transactions. Therefore the correct answer will be D.

The Data definition language is generally used to maintain or define the structure of the database. For example, creating a table, drop table, alter table. In short, we can say that the command of data definition languages is used to work on the table's schemas inside the database.

Whenever we have some related data, information or records, we collect all those related data (or records), put them together, store them in one place, and give that collection a name that is known as a file.

Data abstraction means displaying or sharing only the data that is needed and hiding from all other data until it is necessary to share it. However, the data abstraction level that describes how the data was actually stored in the user's machine (or system) is known as the Physical level. Therefore the correct answer is B.

The data redundancy generally occurs whenever more than one copy of the exact same data exists in several different places. Sometimes it may cause data inconsistency, which can result in an unreliable source of data or information that is not good for anyone.

The New Technology File System was introduced in 1993 for the very first time as a part of new Windows operating systems (Windows NT 3.1).

You may be surprised to know that windows are still using it because of its fast speed and can support files whose size is up to 16TB (16 terabytes), which is much more than that file size supported by the old system.

We can understand the "one to many" relationship as a teacher who may have more than one class to attend.