Which property of an entity can become a column in a table?
Correct Answer: C
Indatabase design,attributesof an entity becomecolumnsin a relational table. Example Usage: For anEmployee entity, attributes might include: CREATE TABLE Employees ( EmployeeID INT PRIMARY KEY, Name VARCHAR(50), Salary DECIMAL(10,2), DepartmentID INT ); * Eachattribute(e.g., Name, Salary) becomes acolumnin the table. Why Other Options Are Incorrect: * Option A (Modality) (Incorrect):Describesoptional vs. mandatoryrelationships, not table structure. * Option B (Uniqueness) (Incorrect):Ensuresdistinct valuesbutis not a column property. * Option D (Non-null values) (Incorrect):Ensures thatcolumns must contain databut doesnot define attributes. Thus, the correct answer isAttribute, as attributes of entities becometable columns.
Question 2
Which statement uses valid syntax for the DELETE statement in SQL?
Correct Answer: B
Thecorrect syntaxfor deleting records from a table in SQL is: sql DELETE FROM table_name WHERE condition; This deletesonly the rowsthat match the condition. Example Usage: sql DELETE FROM Employees WHERE Salary < 30000; * Deletesall employees earning less than $30,000. Why Other Options Are Incorrect: * Option A (Incorrect):Missing FROMkeyword. The correct syntax is DELETE FROM table_name. * Option C (Partially Correct):DELETE FROM table_name;deletes all rows, but it lacks a WHERE clause. * Option D (Incorrect):DELETE *is not validin SQL. The correct command is just DELETE FROM. Thus, the correct answer isDELETE FROM table_name WHERE condition;.
Question 3
What is information independence?
Correct Answer: D
Information independencerefers to theseparation between data storage and data access. It allows a database'slogical structureto be modifiedwithout affecting existing applications. Types of Information Independence: * Logical Data Independence# Ability to change theconceptual schema(e.g., renaming columns, adding new attributes)without modifying applications. * Physical Data Independence# Ability to change thephysical storage structure(e.g., indexing, partitioning)without affecting queries. Example of Logical Data Independence: * Anew columnis added to the Customers table, but existing queriesstill work without modification. Example of Physical Data Independence: * Data is moved to SSD storagefor performance improvement, but queriesrun the same way. Why Other Options Are Incorrect: * Option A (Incorrect):Changing thedatabase type(e.g., MySQL to PostgreSQL) isnotinformation independence. * Option B (Incorrect):Making changes toqueriesis unrelated to database independence. * Option C (Incorrect):Interchanging databases is related todata portability, notinformation independence. Thus, the correct answer isD - An ability to change the organization of data, asinformation independence ensuresmodifications do not disrupt database operations.
Question 4
Which keyword can be used as a clause in an ALTER TABLE statement?
Correct Answer: B
TheALTER TABLEstatement is used to modify an existing database table structure. One common clause is CHANGE, which allows renaming a column and modifying its data type. Example: sql ALTER TABLE Employees CHANGE COLUMN OldName NewName VARCHAR(50); * Option A (Incorrect):DELETE is used to removerows, not alter table structure. * Option B (Correct):CHANGE is avalid clausefor renaming and modifying columns in MySQL and some other databases. * Option C (Incorrect):STOP is not a valid SQL keyword for altering tables. * Option D (Incorrect):AGGREGATE refers to functions like SUM() and AVG(), not table alterations.
Question 5
Where does a primary key traditionally appear in a table?
Correct Answer: B
Bydatabase design conventions, theprimary key is usually placed in the first columnof a table to make it easy to identify and reference. Example Usage: sql CREATE TABLE Employees ( EmpID INT PRIMARY KEY, -- First column (convention) Name VARCHAR(50), Salary DECIMAL(10,2) ); * EmpID is placed as the first columnfor clarity and quick access. Why Other Options Are Incorrect: * Option A (In the table header) (Incorrect):Table headers onlydisplay column names, they do not contain values. * Option C (In the top row) (Incorrect):Thetop row contains data, not theprimary key definition. * Option D (In the last visible column) (Incorrect):While technically possible,placing a primary key at the endisuncommonin database design. Thus, the correct answer isIn the first column, as this is the standard convention in relational databases.
