Data Retrieval language(DRL)

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Data Retrieval language(DRL)

Data Retrieval Language (DRL) is a part of SQL used to retrieve (fetch) data from a database without modifying it.

Main Command: SELECT – used to get data from one or more tables.

Examples:

SELECT * FROM students;
→ Retrieves all records from the students table.

SELECT name, marks FROM students WHERE marks > 60;
→ Retrieves names and marks of students who scored more than 60.

SELECT * FROM students;

→ Retrieves all records from the students table.

SELECT name, marks FROM students WHERE marks > 60;

→ Retrieves names and marks of students who scored more than 60.

Purpose:

● To view data

● To filter required information

● To sort and display data in a useful format Marks-friendly line (for exams):

Data Retrieval Language (DRL) is used to retrieve data from a database. The SELECT command is used in DRL.

Distinct

DISTINCT is used in the SELECT statement to remove duplicate values and display unique records from a column.

Syntax:

SELECT DISTINCT column_name FROM table_name;
Example:
SELECT DISTINCT city FROM students;

SELECT DISTINCT column_name FROM table_name;

Example:

SELECT DISTINCT city FROM students;

→ Displays each city only once, even if it appears many times in the table.

Use: To avoid repeated values & To get unique data

Exam answer (short): DISTINCT is used to retrieve unique values from a column by eliminating duplicate records.

Expression Definition:

An expression in SQL is a combination of columns, constants, operators, and functions that is used to calculate or derive a value.

Examples:

1. Arithmetic expression
SELECT marks + 5 AS new_marks FROM students;

2. Comparison expression
SELECT * FROM students WHERE marks > 60;

3. Logical expression
SELECT * FROM students WHERE marks > 60 AND city = 'Pune';

1. Arithmetic expression

SELECT marks + 5 AS new_marks FROM students;

2. Comparison expression

SELECT * FROM students WHERE marks > 60;

3. Logical expression

SELECT * FROM students WHERE marks > 60 AND city = 'Pune';

Use: To perform calculations, To compare values & To filter data

Exam-friendly line:

An expression in SQL is a formula used to compute or evaluate values using operators and operands.

Definition:An alias is a temporary name given to a column or a table to make the output easy to read. It does not change the original name.

Syntax:

SELECT column_name AS alias_name FROM table_name; (or AS is optional)

Examples:

1. Column alias
SELECT name AS student_name FROM students;

2. Table alias
SELECT s.name FROM students s;

1. Column alias

SELECT name AS student_name FROM students;

2. Table alias

SELECT s.name FROM students s;

Use:

● To improve readability To shorten long names

● Useful in expressions and joins

Exam-friendly line: Alias names are temporary names given to columns or tables using AS for easy identification.

Operators

Definition: Operators are symbols used to perform operations on data in SQL expressions and conditions.

Types of SQL Operators:

Arithmetic Operators

+ , − , * , / , %

Example: SELECT marks + 10 FROM students;

Comparison (Relational) Operators

= , != , > , < , >= , <=

Example: SELECT * FROM students WHERE marks >= 60;

Logical Operators AND , OR , NOT

Example: SELECT * FROM students WHERE marks > 60 AND city = ‘Mumbai’;

Special Operators

IN , BETWEEN , LIKE , IS NULL

Example: SELECT * FROM students WHERE city IN (‘Pune’,’Delhi’); There are three types of operaters

Arithmetic operators

Arithmetic operators are used in SQL to perform mathematical calculations on numeric data. Types of Arithmetic Operators

Operator	Name	Description	Example
+	Addition	Adds two values	marks + 5
–	Subtraction	Subtracts one value from another	marks – 10
*	Multiplication	Multiplies values	marks * 2
/	Division	Divides one value by another salary	marks / 2
%	Modulus	Returns remainder after division	marks % 2

Examples with Explanation

<strong>Addition
</strong>SELECT marks + 5 AS updated_marks FROM students;
→ Adds 5 to each student’s marks.

<strong>Subtraction
</strong>SELECT marks - 3 FROM students;
→ Subtracts 3 from marks.

<strong>Multiplication
</strong>SELECT quantity * price AS total_cost FROM sales;
→ Calculates total cost.

<strong>Division
</strong>SELECT salary / 12 AS monthly_salary FROM employee;
→ Converts yearly salary into monthly salary.

<strong>Modulus
</strong>SELECT marks % 2 FROM students;
→ Shows remainder (useful to check even/odd). Uses of Arithmetic Operators

Addition

SELECT marks + 5 AS updated_marks FROM students;

→ Adds 5 to each student’s marks.

Subtraction

SELECT marks - 3 FROM students;

→ Subtracts 3 from marks.

Multiplication

SELECT quantity * price AS total_cost FROM sales;

→ Calculates total cost.

Division

SELECT salary / 12 AS monthly_salary FROM employee;

→ Converts yearly salary into monthly salary.

Modulus

SELECT marks % 2 FROM students;

→ Shows remainder (useful to check even/odd). Uses of Arithmetic Operators

To calculate totals, averages, discounts To modify numeric values in queries Used in SELECT, WHERE, and UPDATE

*Arithmetic operators in SQL are used to perform mathematical calculations on numeric data. They include +, −, , /, and %. These operators are commonly used in expressions to calculate totals, differences, and other numeric results.

Relational (Comparison) Operators

Relational operators are used in SQL to compare two values. They return TRUE or FALSE and are mainly used in the WHERE clause.

Operator	Description	Example
=	Equal to	marks = 60
!= or <>.	Not equal to	marks != 50
>	Greater than	marks > 60
<	Less than.	marks < 40
>=	Greater than Or equal to.	marks >= 75
<=	Less than or equal to	marks <= 35

Examples with Explanation

Equal to
SELECT * FROM students WHERE city = 'Pune';
→ Selects students from Pune.


Greater than
SELECT * FROM students WHERE marks > 60;
→ Selects students scoring above 60.


Less than or equal to
SELECT * FROM students WHERE age <= 18;
→ Selects students aged 18 or below.

Equal to

SELECT * FROM students WHERE city = 'Pune';

→ Selects students from Pune.

Greater than

SELECT * FROM students WHERE marks > 60;

→ Selects students scoring above 60.

Less than or equal to

SELECT * FROM students WHERE age <= 18;

→ Selects students aged 18 or below.

Uses

● To filter records

● To apply conditions

● Used with WHERE, HAVING

> Relational operators are used to compare values in SQL. They include =, !=, >, <, >= and

<= and help in filtering records based on conditions.

Logical Operators

Logical operators are used to combine multiple conditions in a SQL query. They return TRUE or FALSE.

Types of Logical Operators

<strong>AND
</strong>Returns TRUE when all conditions are true.
SELECT * FROM students
WHERE marks > 60 AND city = 'Pune';

<strong>OR
</strong>Returns TRUE when any one condition is true.
SELECT * FROM students
WHERE marks > 60 OR city = 'Mumbai';

<strong>NOT
</strong>Reverses the condition.
SELECT * FROM students WHERE NOT city = 'Delhi';

AND

Returns TRUE when all conditions are true.

SELECT * FROM students

WHERE marks > 60 AND city = 'Pune';

OR

Returns TRUE when any one condition is true.

SELECT * FROM students

WHERE marks > 60 OR city = 'Mumbai';

NOT

Reverses the condition.

SELECT * FROM students WHERE NOT city = 'Delhi';

Lavanya Nandagiri

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Data Retrieval language(DRL)

Data Retrieval Language (DRL) is a part of SQL used to retrieve (fetch) data from a database without modifying it.

Main Command: SELECT – used to get data from one or more tables.

Examples:

Purpose:

● To view data

● To filter required information

● To sort and display data in a useful format Marks-friendly line (for exams):

Data Retrieval Language (DRL) is used to retrieve data from a database. The SELECT command is used in DRL.

Distinct

DISTINCT is used in the SELECT statement to remove duplicate values and display unique records from a column.

Syntax:

→ Displays each city only once, even if it appears many times in the table.

Use: To avoid repeated values & To get unique data

Exam answer (short): DISTINCT is used to retrieve unique values from a column by eliminating duplicate records.

Expression Definition:

An expression in SQL is a combination of columns, constants, operators, and functions that is used to calculate or derive a value.

Examples:

Use: To perform calculations, To compare values & To filter data

Exam-friendly line:

An expression in SQL is a formula used to compute or evaluate values using operators and operands.

Definition:An alias is a temporary name given to a column or a table to make the output easy to read. It does not change the original name.

Syntax:

SELECT column_name AS alias_name FROM table_name; (or AS is optional)

Examples:

Use:

● To improve readability To shorten long names

● Useful in expressions and joins

Exam-friendly line: Alias names are temporary names given to columns or tables using AS for easy identification.

Operators

Definition: Operators are symbols used to perform operations on data in SQL expressions and conditions.

Types of SQL Operators:

Arithmetic Operators

+ , − , * , / , %

Example: SELECT marks + 10 FROM students;

Comparison (Relational) Operators

= , != , > , < , >= , <=

Example: SELECT * FROM students WHERE marks >= 60;

Logical Operators AND , OR , NOT

Example: SELECT * FROM students WHERE marks > 60 AND city = ‘Mumbai’;

Special Operators

IN , BETWEEN , LIKE , IS NULL

Example: SELECT * FROM students WHERE city IN (‘Pune’,’Delhi’); There are three types of operaters

Arithmetic operators

Arithmetic operators are used in SQL to perform mathematical calculations on numeric data. Types of Arithmetic Operators

Examples with Explanation

To calculate totals, averages, discounts To modify numeric values in queries Used in SELECT, WHERE, and UPDATE

*Arithmetic operators in SQL are used to perform mathematical calculations on numeric data. They include +, −, , /, and %. These operators are commonly used in expressions to calculate totals, differences, and other numeric results.

Relational (Comparison) Operators

Relational operators are used in SQL to compare two values. They return TRUE or FALSE and are mainly used in the WHERE clause.

Examples with Explanation

● To filter records

● To apply conditions

● Used with WHERE, HAVING

> Relational operators are used to compare values in SQL. They include =, !=, >, <, >= and

<= and help in filtering records based on conditions.

Logical Operators

Logical operators are used to combine multiple conditions in a SQL query. They return TRUE or FALSE.

Types of Logical Operators

Uses

To apply multiple conditions To filter data accurately

Used mainly in WHERE and Having

> Logical operators in SQL are used to combine conditions. AND, OR, and NOT are the logical operators that help in decision making.

Author : Lavanya Nandairi

LinkedIn : https://www.linkedin.com/in/lavanya-nandagiri-817194375/

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