Advanced SQL (DTAN 6120)

Correct Answer C. INTEGER

Explanation

The INTEGER (INT) data type is the primary data type used for storing whole numbers in MySQL. It supports both signed and unsigned values, making it suitable for storing IDs, counts, and other numeric values that do not require decimal precision. INTEGER provides efficient storage and indexing, making it ideal for most applications requiring whole numbers.

Why Other Options Are Wrong

A. FLOAT is used to store approximate decimal values and is prone to rounding errors, making it unsuitable for storing precise whole numbers. It is commonly used in scientific and statistical computations rather than for primary key values or count-based data.

B. DOUBLE is another floating-point data type, but it consumes more storage and is typically used for high-precision decimal values, not whole numbers. Unlike INTEGER, DOUBLE supports fractional values, which are not required for storing integer-based data.

D. DECIMAL is specifically designed for fixed-point precision, making it useful for financial and monetary calculations, not whole numbers. While it can store integer values, its extra precision handling makes it unnecessary for non-decimal data storage.

Correct Answer C. The database will reject the entry and return an error message.

Explanation

A unique constraint ensures that no two rows in a table have the same value in the specified column. If a user attempts to insert a duplicate email, the database will enforce the constraint by rejecting the entry and displaying an error message. This helps maintain data integrity by preventing duplicate records.

Why Other Options Are Wrong

A. The database will accept the duplicate entry without any issues.

The database does not allow duplicate entries in a column with a unique constraint. If a user tries to insert a duplicate value, the system enforces the uniqueness rule and prevents the operation from being completed successfully. Allowing duplicates would violate the integrity of the constraint.

B. The database will automatically change the duplicate email to a unique value.

The database does not automatically modify user data to make it unique. It is the responsibility of the user or application logic to handle duplicate entries before inserting them. The database enforces constraints but does not alter input values without explicit instructions.

D. The database will allow the entry but mark it as a duplicate

The database does not "mark" an entry as a duplicate while allowing it; instead, it prevents the duplicate from being stored in the first place. If duplicates were allowed and only marked, it would defeat the purpose of using a unique constraint.

Correct Answer B. It ensures that all records have a valid entry for that column.

Explanation

The NOT NULL constraint ensures that a column cannot have NULL values, meaning every record must have a valid entry in that field. This is crucial for maintaining data integrity, as certain fields, such as primary keys, email addresses, or order numbers, must always contain valid data. Without NOT NULL, essential fields could be left blank, leading to incomplete or inconsistent records.

Why Other Options Are Wrong

A. It prevents duplicate entries in a column.

The NOT NULL constraint does not prevent duplicate entries; that is the role of the UNIQUE constraint. A column with NOT NULL can still contain duplicate values as long as no NULLs are present. Preventing duplicates requires an additional constraint, such as UNIQUE or PRIMARY KEY.

C. It allows for flexible data entry without restrictions.

The NOT NULL constraint does not allow for flexible data entry, as it forces a value to be provided. While flexibility is important in some cases, NOT NULL ensures that critical fields are always populated, preventing issues caused by missing data.

D. It automatically fills in missing data with default values.

The NOT NULL constraint does not automatically fill in missing data. If a column is NOT NULL and no value is provided, the database will return an error instead of inserting a default value. Default values must be explicitly set using the DEFAULT keyword.

Correct Answer B. BLOB can store large binary data; for example, storing images or videos.

Explanation

A Binary Large Object (BLOB) is a data type designed to store large binary data, including images, videos, audio files, and other multimedia content. Since BLOBs store raw binary data, they are commonly used in applications that require storing non-textual information within a database, such as profile pictures, scanned documents, and media archives.

Why Other Options Are Wrong

A. BLOB can store text data; for example, storing user comments.

BLOB is not meant for storing text data; TEXT or VARCHAR data types are used instead. Although BLOB can technically store text in binary format, it does not support text-based operations like searching or sorting efficiently.

C. BLOB can store structured data; for example, storing tables.

BLOB does not store structured data like tables; relational databases store structured data using tables with defined columns and constraints. Storing tables as binary objects would make it impossible to perform relational queries and indexing.

D. BLOB can store numerical data; for example, storing statistics.

BLOB does not store numerical data; INTEGER, DECIMAL, or FLOAT are used for storing numeric values. Numbers stored in a BLOB format cannot be used for arithmetic operations, making it inefficient for handling statistics or calculations.

Correct Answer C. It enables administrators to control user permissions effectively.

Explanation

The GRANT command in SQL is part of Data Control Language (DCL) and is used to assign specific privileges to users. Administrators can grant permissions such as SELECT, INSERT, UPDATE, and DELETE to control who can access or modify data. This command plays a crucial role in database security by preventing unauthorized access and enforcing access control policies.

Why Other Options Are Wrong

A. It restricts access to the database entirely.

The GRANT command does not restrict access but grants permissions to users. To restrict access, the REVOKE command is used instead. Security policies rely on both GRANT and REVOKE commands to manage database access effectively.

B. It allows users to create new databases.

While GRANT can allow a user to execute commands, it does not specifically create new databases. The CREATE DATABASE statement is responsible for database creation, while GRANT is used to assign privileges on existing databases or tables.

D. It automatically backs up the database.

The GRANT command does not perform database backups. Backups are managed using administrative tools, scheduled jobs, or SQL commands like BACKUP DATABASE (SQL Server) or mysqldump (MySQL). GRANT focuses on user access control, not data preservation.

Correct Answer B. Criteria determine which records are included in the result set.

Explanation

The SELECT statement retrieves data from a database, and criteria (specified in the WHERE clause) filter which records should be included in the result set. By applying conditions such as comparisons (=, >, <), logical operators (AND, OR), and pattern matching (LIKE), users can extract only the relevant data. Criteria improve query efficiency by reducing the number of returned rows, making data analysis and reporting more precise.

Why Other Options Are Wrong

A. Criteria are used to define the structure of the database.

Criteria do not define the structure of the database; instead, they determine which records meet specific conditions in a query. The structure of a database is defined by schemas, tables, and columns, not by filtering conditions in SELECT statements.

C. Criteria are irrelevant to the SELECT command.

Criteria are not irrelevant to the SELECT command; they play a crucial role in filtering data. Without criteria, a SELECT query retrieves all records from a table, which may not always be efficient or useful for analysis.

D. Criteria are only used for updating records.

Criteria are not only used for updating records; they are fundamental to retrieving specific data in SELECT queries. Although criteria are also used in UPDATE and DELETE statements, their role in SELECT queries is essential for filtering results.

Correct Answer C. INT(11)

Explanation

The INT data type in MySQL is used to store whole numbers, including both signed and unsigned integers. The (11) in INT(11) specifies the display width, not the storage size. By default, INT can store values from -2,147,483,648 to 2,147,483,647 (signed) or 0 to 4,294,967,295 (unsigned), making it suitable for large numeric values without decimals.

Why Other Options Are Wrong

A. VARCHAR

VARCHAR is used to store text and character strings, not whole numbers. Attempting to store numeric values in a VARCHAR column can lead to performance issues and inefficient storage usage.

B. TEXT

TEXT is designed for large text storage, such as comments, descriptions, or articles, and is not optimized for numerical calculations. Using TEXT for numbers would prevent sorting, indexing, and mathematical operations.

D. FLOAT

FLOAT is a floating-point data type, meaning it is used to store decimal values, not strictly whole numbers. It is susceptible to rounding errors, making it unsuitable for exact numerical calculations, especially in financial applications.

Correct Answer B. To communicate with the database for data manipulation and management.

Explanation

SQL (Structured Query Language) is used to retrieve, insert, update, and delete data in relational databases. It provides a standardized way to interact with database management systems (DBMS), allowing users to manipulate data, define schemas, and manage transactions. SQL plays a crucial role in querying and maintaining relational databases.

Why Other Options Are Wrong

A. To store data securely

While SQL supports security features such as user permissions and access control, its primary purpose is not security. Security is enforced through Data Control Language (DCL) and database configuration settings, while SQL mainly focuses on querying and managing data.

C. To create database backups

SQL commands like BACKUP DATABASE exist in some systems, but database backups are primarily handled by administrative tools and scheduled maintenance processes. SQL itself is not solely responsible for backups, as database systems use automated scripts, replication, and recovery features.

D. To design user interfaces for databases

SQL does not design user interfaces; UI development is handled through frontend programming languages like HTML, JavaScript, and frameworks like React or Angular. SQL supports data interaction and retrieval, but designing graphical interfaces requires separate tools.

Correct Answer B. To ensure data is accurate and trustworthy.

Explanation

Data quality is crucial for accurate reporting, decision-making, and operational efficiency. High-quality data is complete, consistent, accurate, and timely, ensuring that businesses can trust the information used in analytics, transactions, and strategic planning. Poor data quality leads to errors, inefficiencies, and incorrect conclusions.

Why Other Options Are Wrong

A. To enhance the speed of data retrieval

While structured and high-quality data may indirectly improve retrieval speed, data quality focuses more on accuracy and consistency rather than query performance. Query optimization techniques, such as indexing and caching, affect retrieval speed more directly.

C. To reduce the size of the database

Data quality efforts do not necessarily reduce database size; they prevent redundant or incorrect data but may also increase the volume of stored data due to proper data retention policies.

D. To simplify SQL command usage

High-quality data does not simplify SQL command usage; SQL complexity depends on query structure and database design rather than data accuracy. However, structured and well-organized data makes queries more reliable.