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InSQL syntax, the FROM clause is the first clause that follows SELECT. It specifies the table(s) from which the data will be retrieved.

Example:

sql

SELECT name, salary FROM Employees;

Option A (Correct):The FROM clauseimmediately followsthe SELECT clause in MySQL.

Option B (Incorrect):VALUE is not a valid clause in MySQL SELECT statements.

Option C (Incorrect):WHERE is used to filter recordsafter specifying the table in FROM.

Option D (Incorrect):TABLE is not a valid clause following SELECT in SQL.

In databases, primary keys are oftenset to auto-incrementso that new rows automatically receive unique values. However,one common error is manually inserting a value into an auto-incremented primary key column, whichoverrides the automatic numberingand may cause conflicts.

Example of Auto-Increment Setup:

sql

CREATE TABLE Users (

UserID INT AUTO_INCREMENT PRIMARY KEY,

Username VARCHAR(50)

);

Incorrect Insert (Error-Prone Approach):

sql

INSERT INTO Users (UserID, Username) VALUES (100, 'Alice');

Thismanually overrides the auto-increment, which can lead toduplicate key errors.

Correct Insert (Avoiding Errors):

sql

INSERT INTO Users (Username) VALUES ('Alice');

Thedatabase assigns UserID automatically, preventing conflicts.

Why Other Options Are Incorrect:

Option B (Failing to set a numeric value) (Incorrect):The databaseautomatically assignsvalues when AUTO_INCREMENT is used.

Option C (Designating multiple primary keys) (Incorrect):Whileincorrect, most databases will prevent this at creation time.

Option D (Forgetting to specify which is the auto-increment column) (Incorrect):If AUTO_INCREMENT is set, the database handles numbering automatically.

Thus, the most common error isInserting a value and overriding auto-increment, which can causeduplicate key errors and data inconsistencies.

TheONkeyword specifies the field used by anindexwhen creating it in SQL.

Example Usage:

sql

CREATE INDEX idx_employee_name

ON Employees(Name);

Here, an indexidx_employee_nameis createdon the Name column.

Thisimproves query performancewhen filtering by Name.

Why Other Options Are Incorrect:

Option B (IN) (Incorrect):Used in queries to match values in a set, not for indexing.

Option C (UNIQUE) (Incorrect):Ensures a column has unique values but doesnot define an index field.

Option D (CHECK) (Incorrect):Used forvalidating column values, not for indexing.

Thus, the correct answer isON, as it defines thecolumn on which an index is created.

Thecorrect syntaxfor inserting a new row into a table follows this structure:

Standard SQL INSERT Syntax:

sql

INSERT INTO TableName (Column1, Column2, ...)

VALUES (Value1, Value2, ...);

For this scenario:

sql

INSERT INTO Employee (Name) VALUES ('John Doe');

Why Other Options Are Incorrect:

Option A (Incorrect):Uses incorrect syntax { ... }, which isnot valid SQL syntax.

Option C (Incorrect):Does not specify the column name, whichcauses an error.

Option D (Incorrect):Misses theINTOkeyword, which is required in standard SQL.

Thus, the correct syntax isOption B, ensuring aproperly formatted insert statement.

Attributesin a databaserepresent the properties (names, values, or characteristics) of an entity.

Example Usage:

In aStudentstable, attributes might include:

StudentID (Primary Key), Name, Age, Major

Here,Name is an attributedescribing the entityStudent.

Why Other Options Are Incorrect:

Option A (Synonyms) (Incorrect):Synonyms in SQL allow different names for the same object but arenot attributes.

Option C (Repositories) (Incorrect):A repository stores data butdoes not define attributes.

Option D (Relationships) (Incorrect):Relationships defineconnections between entities, not their attributes.

Thus, the correct answer isNames, asattributes define entity properties.

This query performs ajoin operationwhere records from the Make table and Model table are combined based on the condition Make.ModelID = Model.ID. This conditiontests for equality, which is the definition of anEQUIJOIN.

Types of Joins in SQL:

EQUIJOIN (Correct Answer):

Uses an equality operator (=) to match rows between tables.

Equivalent to an INNER JOIN ON condition.

Example:

sql

SELECT *

FROM Employees

JOIN Departments ON Employees.DeptID = Departments.ID;

NON-EQUIJOIN (Incorrect):

Usescomparison operators other than =(e.g., <, >, BETWEEN).

Example:

sql

SELECT *

FROM Employees e

JOIN Salaries s ON e.Salary > s.MedianSalary;

SELF JOIN (Incorrect):

A table is joined withitselfusing table aliases.

Example:

sql

SELECT e1.Name, e2.Name AS Manager

FROM Employees e1

JOIN Employees e2 ON e1.ManagerID = e2.ID;

CROSS JOIN (Incorrect):

ProducesCartesian product(each row from Table A combines with every row from Table B).

Example:

sql

SELECT *

FROM Employees

CROSS JOIN Departments;

Thus, since our given query uses anequality condition (=) to join two tables, it is anEQUIJOIN.

Analiasis used in SQL to give atemporaryname to a table or column within a query. It makes queries more readable and helps in cases where a table needs to be referenced multiple times (e.g., in aself-join).

Example Usage:

sql

SELECT e.Name, d.DepartmentName

FROM Employees AS e

JOIN Departments AS d

ON e.DeptID = d.ID;

Here,Employees is aliased as eandDepartments as d, making the query shorter and clearer.

Why Other Options Are Incorrect:

Option A (HAVING) (Incorrect):Used to filter grouped results, not create aliases.

Option B (NEW) (Incorrect):Not a valid SQL keyword for aliasing.

Option D (UNION) (Incorrect):Combines result sets but does not rename tables.

Thus, the correct answer isALIAS, which allows fortemporary naming of tables or columns.

Aunary relationship(also known as arecursive relationship) occurs when an entityrelates to itself.

Example Usage:

Employees and Managers:

sql

CREATE TABLE Employees (

EmpID INT PRIMARY KEY,

Name VARCHAR(50),

ManagerID INT,

FOREIGN KEY (ManagerID) REFERENCES Employees(EmpID)

);

Here, ManagerIDreferences another Employee→ aunary (self-referential) relationship.

Why Other Options Are Incorrect:

Option A (Modality) (Incorrect):Describesoptional vs. mandatoryrelationships, not self-referencing.

Option C (Cardinality) (Incorrect):Defines how many instances relate,not the type of relationship.

Option D (Binary) (Incorrect):Binary relationships involvetwo different entities, not self-referencing.

Thus, the correct answer isUnary, as it describesrelationships within the same entity type.