Data Base MCQS

A table is in its 3rd NF if it has already completed in 2NF, and non-key attributes are not dependent on any non-key attributes. This means that all non-key attributes must depend on primary key. When a table represents a single entity, the primary key will identify the instance row and all attributes in 3NF are dependent on the primary key. So, the primary key in the 3th NF captures the whole information of this single entity.

Inner Join and Non-Matched Tuples

Inner join returns only the rows that have matching values in both tables. This means that any tuples that don't have a corresponding match in the other table are excluded from the result.

Other Join Types

Left outer join: Preserves all tuples from the left table, even if there are no matches in the right table.

Right outer join: Preserves all tuples from the right table, even if there are no matches in the left table.

Natural join: Similar to inner join, but only considers columns with the same name for matching.

In summary, while outer joins include unmatched tuples in the result, inner join strictly focuses on matching rows and discards any that don't have a corresponding match.

Relational Algebra is a Procedural Language

Relational algebra is indeed a procedural language. This means it specifies a sequence of operations that must be performed in a specific order to achieve the desired result. It's like providing a recipe for manipulating data within a database.

Why not the others?

Domain relational calculus and tuple relational calculus are declarative languages. They specify what data is desired without specifying how to compute it.

Query language is a broad term that can encompass both procedural and non-procedural languages.

Key point: Relational algebra provides a step-by-step approach to manipulating data, making it a procedural language.

Breakdown of other options:

DELETE FROM teaches WHERE Id = 'Null';: This command would only delete rows where the Id column has a NULL value. It wouldn't delete all rows.

REMOVE TABLE teaches;: There's no standard SQL command named REMOVE.

DROP TABLE teaches;: This command would delete the entire table structure, including its data and definition, which is typically not desired when you just want to clear the data.

So, the simple and effective way to delete all data from the teaches table is by using DELETE FROM teaches;.

Identifying Set

A weak entity set must be associated with an identifying set for it to be meaningful.

Here's a breakdown:

Weak Entity Set: An entity set that cannot exist independently and depends on another entity set (strong entity set) for its existence.

Identifying Set: A set of attributes in a strong entity set that uniquely identifies each entity in the weak entity set.

Essentially, a weak entity set needs a "parent" strong entity set to provide it with a unique identifier. This is because a weak entity set doesn't have sufficient attributes on its own to form a primary key.

Example:

Strong Entity Set: Employee (Employee_ID, Employee_Name, Department)

Weak Entity Set: Dependent (Dependent_Name, Relationship, Employee_ID)

DROP TABLE is the SQL command used to remove an entire relation (table) from a database.

Here's a breakdown of why the other options are incorrect:

DELETE: This command removes rows (tuples) from a table, but it doesn't remove the table itself.

PURGE: This command is not a standard SQL command. It might exist in specific database systems with particular functionalities, but it's not generally used for removing tables.

REMOVE: This is also not a standard SQL command for removing tables.

So, DROP TABLE is the correct choice for permanently deleting a table from a database.

A super key is actually a set of one or more attributes that uniquely identify a record.

Breakdown of the options:

Super key: Any set of attributes that uniquely identifies a tuple (row) in a relation (table).

Candidate key: A minimal super key (no unnecessary attributes).

Primary key: A chosen candidate key to uniquely identify a record.

Foreign key: A field in one table that refers to the primary key in another table.

So, while a super key is a broader term encompassing any set of attributes that uniquely identify a record, it's not the most specific or commonly used term. Candidate key or primary key would be more appropriate in most cases.

DML (Data Manipulation Language) is the language component responsible for manipulating data within a database. This includes the operations you mentioned:

Querying data: Retrieving information from the database.

Inserting data: Adding new records to the database.

Deleting data: Removing existing records from the database.

Altering data: Modifying the values of existing records.

Brief overview of other options:

DDL (Data Definition Language): Defines the structure of the database, including creating, modifying, and dropping tables, indexes, and other database objects.

DCL (Data Control Language): Deals with access control to the database, granting or revoking privileges to users.

TCL (Transaction Control Language): Manages the integrity and consistency of data through transactions (commit, rollback, savepoint).

So, DML is the correct choice for performing actions on the data itself.

A DBMS acts as an interface between a database application and the database.

Here's a breakdown:

Database Application: This is the software that interacts with the user and provides a way to access and manipulate the data in the database. Examples include accounting software, inventory management systems, or customer relationship management (CRM) tools.

Database: This is the underlying storage structure that holds the data. It's where the information is physically stored.

Role of the DBMS:

Translation: The DBMS translates requests from the application into operations that the database can understand.

Data Management: It handles tasks like data storage, retrieval, updating, and deletion.

Security: It ensures data integrity, security, and concurrency control.

By acting as this intermediary, the DBMS simplifies the process for application developers and users, allowing them to focus on their specific needs without worrying about the complexities of data management.

A high-speed, large capacity disk is the most critical hardware component for a database management system (DBMS).

Here's why:

Data Storage: A DBMS is designed to store and manage vast amounts of data. A large capacity disk provides the necessary space to accommodate the growing database.

Performance: High-speed disks enable rapid data access and retrieval. This is essential for efficient database operations like querying, updating, and deleting data.

Reliability: Databases often contain critical information. A reliable disk ensures data integrity and prevents data loss.

While other components like a monitor, printer, or microphone are important for interacting with the DBMS, they are not as critical to its core functionality as the disk.

Therefore, option b) is indeed the correct answer.