Online Data-Management-Foundations Questions Video

Anintangible entityis an entity that does not have a physical presence but still holds meaning in a database. These entities representconcepts, relationships, or abstract datathat exist in a logical sense.

Example Usage in Databases:

Customer Loyalty Status (Gold, Silver, Bronze)

Theloyalty levelis anintangible entitysince it is derived from other data (purchase history).

Online User Sessions

Asession IDexistslogically in the systembut does not have a tangible presence like a product or employee.

Why Other Options Are Incorrect:

Option A (Concrete entity) (Incorrect):No such formal term in database design.

Option B (Tangible entity) (Incorrect):Represents somethingphysical, like anemployeeorproduct.

Option D (Physical entity) (Incorrect):Refers todata stored on disk, like database tables or indexes.

Thus, the correct answer isIntangible entity, as it only exists in a logical sense within the database.

Toadd a primary key constraint after table creation, we use theALTER TABLEstatement.

Example Usage:

sql

ALTER TABLE Employees

ADD CONSTRAINT PK_Employees PRIMARY KEY (EmpID);

Thisaddsa primary key to the EmpID columnafter the table was created.

Why Other Options Are Incorrect:

Option B (CREATE TABLE) (Incorrect):Used for defining constraintsduringtable creation, not after.

Option C (UPDATE) (Incorrect):Modifiesrow values, not constraints.

Option D (INSERT INTO) (Incorrect):Used toadd datato a table, not modify constraints.

Thus, the correct answer isALTER TABLE, as itmodifies table structure to add a primary key constraint.

AFull Join (FULL OUTER JOIN)selectsall records from both tables, filling in NULL values where there is no match. This ensures that no data is lost from either table.

Example Usage:

sql

SELECT Employees.Name, Departments.DepartmentName

FROM Employees

FULL OUTER JOIN Departments ON Employees.DeptID = Departments.ID;

This query retrievesall employees and all departments, even if an employeehas no assigned departmentor a departmenthas no employees.

Types of Joins:

FULL OUTER JOIN (Correct Answer)→ Includesall rows from both tables, filling missing values with NULL.

LEFT JOIN (Incorrect)→ Includesall rows from the left tableandmatching rows from the right table.

RIGHT JOIN (Incorrect)→ Includesall rows from the right tableandmatching rows from the left table.

CROSS JOIN (Incorrect)→ Produces aCartesian product(each row from one table is combined with every row from another table).

Thus, the correct answer isFULL JOIN, whichensures that all rows from both tables appear in the result.

Avalid SELECT statementin SQL follows this basic syntax:

sql

SELECT column1, column2

FROM table_name

WHERE condition;

The correct optionDfollows this syntaxcorrectly.

Why Other Options Are Incorrect:

Option A (Incorrect):SQL does not usedouble quotes(") around column/table names unless explicitly required in some databases.

Option B (Incorrect):The WHERE clausemust appear after the FROM clause.

Option C (Incorrect):ALL isnota valid keyword in standard SQL queries.

Thus,Option Dfollows the correct SQL syntax.