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.

TheCHECKconstraint is used in SQL toenforce ruleson a column's values. It ensures that data inserted into a table meets specified conditions, such as range restrictions or logical rules.
Example Usage:
sql
CREATE TABLE Employees (
ID INT PRIMARY KEY,
Name VARCHAR(50),
Salary INT CHECK (Salary BETWEEN 30000 AND 150000)
);
* This constraint ensures thatsalary values fall between 30,000 and 150,000.
* If an INSERT or UPDATE statement tries to set Salary = 20000, itfailsbecause it does notmeet the CHECK condition.
Why Other Options Are Incorrect:
* Option B (FROM) (Incorrect):Used in SELECT statements, not for constraints.
* Option C (WHERE) (Incorrect):Filters rows in queries butdoes not enforce constraints.
* Option D (SET) (Incorrect):Used for updating records (UPDATE table_name SET column = value) butnot for defining constraints.
Thus,CHECK is the correct answer, as it ensures that column values remain within an expected range.

Aforeign keyis a column (or a set of columns) that establishes arelationship between two tablesby referencing theprimary key of another table.
Example Usage:
sql
CREATE TABLE Departments (
DeptID INT PRIMARY KEY,
DeptName VARCHAR(50)
);
CREATE TABLE Employees (
EmpID INT PRIMARY KEY,
Name VARCHAR(50),
DeptID INT,
FOREIGN KEY (DeptID) REFERENCES Departments(DeptID)
);
* DeptID in Employees is a foreign key, referencing DeptID in Departments.
* Ensuresreferential integrity# DeptID in Employeesmust existin Departments.
Why Other Options Are Incorrect:
* Option A (Super key) (Incorrect):Asuper keyis any set of columns that uniquely identifies a row, but itdoes not reference another table.
* Option B (Simple key) (Incorrect):Asimple keyis asingle-column primary key, not a reference to another table.
* Option C (Composite key) (Incorrect):Acomposite keyconsists ofmultiple columnsbut does not necessarily reference another table.
Thus, the correct answer isForeign key, as it establishes aconnection between two tables.

Anindex scanis a database operation thatquickly locates table blocksusing anindexrather than scanning the entire table. It significantly improves query performance.
Example Usage:
sql
SELECT * FROM Employees WHERE EmployeeID = 105;
* If EmployeeID isindexed, the database uses anindex scantoquickly find the record.
Why Other Options Are Incorrect:
* Option A (Binary search) (Incorrect):A searching algorithm, but not a database operation.
* Option B (Table scan) (Incorrect):Scans theentire table, which isslowerthan an index scan.
* Option C (Fan-out) (Incorrect):Refers tobranching in B-Treesbut doesnot locate table blocks directly.
Thus, the correct answer isIndex scan, as it efficiently locates table blocks.

Binary searchis an algorithm that finds a search value byrepeatedly dividing the search space into two halves. It is commonly used inindexed searches.
Example Usage in Databases:
* B-Trees and B+ Trees(used in database indexing) applybinary searchto navigate the index efficiently.
* If searching for ID = 50 in asorted list of IDs, binary search:
* Splits the list into two halves.
* Checks the middle value.
* Eliminates half of the dataset.
* Repeats until the value is found.
Why Other Options Are Incorrect:
* Option A (Table scan) (Incorrect):Readsevery row,much slowerthan binary search.
* Option C (Index scan) (Incorrect):Uses indexes but does not necessarily apply binary search.
* Option D (Fan-out) (Incorrect):Describesbranching in B-Trees, not searching.
Thus, the correct answer isBinary search, as it repeatedlysplits the indexin two.