Complete Guide to MySQL Functions: String, Numeric, User-Defined & Stored Functions Great 2025

Complete Guide to MySQL Functions: MySQL is not just a database for storing and retrieving data—it also provides powerful built-in functions that allow you to manipulate and format data efficiently. Functions in MySQL return a result after performing specific operations, and they can be categorized into different types based on their functionality.

This article covers string functions, numeric functions, stored functions, and user-defined functions in MySQL with practical examples.

Table of Contents

1. What Are MySQL Functions?
2. Why Use MySQL Functions?
3. Types of MySQL Functions
   • String Functions
   • Numeric Functions
   • Stored Functions
   • User-Defined Functions
4. MySQL String Functions with Examples
5. MySQL Numeric Functions with Examples
6. MySQL Stored Functions with Examples
7. MySQL User-Defined Functions Overview
8. Summary

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1. What Are MySQL Functions?

Complete Guide to MySQL Functions: A function in MySQL is a predefined or user-defined operation that performs a calculation and returns a value. Some functions require input parameters, while others do not.

For example, if you want to change the default YYYY-MM-DD date format to DD-MM-YYYY, you can use the built-in DATE_FORMAT function.

sql

SELECT DATE_FORMAT(‘2024-03-21’, ‘%d-%m-%Y’);

2. Why Use MySQL Functions?

• Data Formatting: Functions help in modifying the data format directly within SQL queries.
• Performance Improvement: Using MySQL functions reduces the need for additional programming logic in application code.
• Consistency: Ensures uniform data processing across different applications accessing the same database.
• Reduced Network Load: Instead of sending raw data to the application for processing, MySQL functions return pre-processed data, reducing network traffic.

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3. Types of MySQL Functions

A) String Functions

Complete Guide to MySQL Functions: String functions manipulate text-based data in MySQL.

Example: Convert movie titles to uppercase using UCASE():

sql

SELECT movie_id, title, UCASE(title) AS upper_case_title FROM movies;

movie_id	title	upper_case_title
4	Code Name Black	CODE NAME BLACK
5	Daddy’s Little Girls	DADDY’S LITTLE GIRLS
7	Davinci Code	DAVINCI CODE

Other common string functions:

• LCASE() – Converts text to lowercase.
• CONCAT(str1, str2, …) – Combines multiple strings.
• LENGTH() – Returns the length of a string.

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B) Numeric Functions

Complete Guide to MySQL Functions: Numeric functions perform arithmetic operations in MySQL.

Arithmetic Operators in MySQL

Operator	Description	Example	Output
DIV	Integer division	SELECT 23 DIV 6;	3
/	Division	SELECT 23 / 6;	3.8333
–	Subtraction	SELECT 23 – 6;	17
+	Addition	SELECT 23 + 6;	29
*	Multiplication	SELECT 23 * 6;	138
% or MOD	Modulus	SELECT 23 % 6;	5

Common Numeric Functions

FLOOR(value) – Rounds a number down to the nearest integer.

sql

SELECT FLOOR(23 / 6) AS floor_result;

•  Output: 3
  

ROUND(value) – Rounds a number to the nearest whole number.

sql

SELECT ROUND(23 / 6) AS round_result;

•  Output: 4
  

RAND() – Generates a random number.

sql

SELECT RAND() AS random_result;

•  Output: 0.84723 (varies every time)
  

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C) Stored Functions

Complete Guide to MySQL Functions: Stored functions in MySQL are user-defined functions created inside the database server and can be reused in SQL queries.

Syntax for Creating a Stored Function

sql

CREATE FUNCTION function_name(parameter1 TYPE)

RETURNS return_type

DETERMINISTIC

BEGIN

   — Function logic here

   RETURN value;

END;

Example: Checking Overdue Movie Returns

Complete Guide to MySQL Functions: The following function checks whether a rented movie is past its return date:

sql

DELIMITER |

CREATE FUNCTION is_movie_overdue(return_date DATE)

  RETURNS VARCHAR(3)

  DETERMINISTIC

  BEGIN

     DECLARE result VARCHAR(3);

     IF CURDATE() > return_date THEN

        SET result = ‘Yes’;

     ELSE

        SET result = ‘No’;

     END IF;

     RETURN result;

  END |

DELIMITER ;

Using the Function in a Query

sql

SELECT movie_id, return_date, CURDATE(), is_movie_overdue(return_date) FROM movierentals;

movie_id	return_date	CURDATE()	is_movie_overdue
2	2024-02-15	2024-03-21	Yes
3	2024-04-10	2024-03-21	No

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D) User-Defined Functions (UDFs)

Complete Guide to MySQL Functions: Unlike stored functions, user-defined functions (UDFs) are created outside MySQL using languages like C or C++ and then integrated into the database.

UDFs provide additional functionality not available in built-in MySQL functions. They must be compiled and installed in MySQL before use.

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8. Summary

• Complete Guide to MySQL Functions: MySQL Functions enhance data manipulation capabilities within SQL queries.
• Built-in functions include string functions (e.g., UCASE()), numeric functions (e.g., ROUND()), and date functions (e.g., DATE_FORMAT()).
• Stored functions allow users to define reusable logic inside MySQL.
• User-defined functions (UDFs) extend MySQL functionality using external programming languages.

Using MySQL functions efficiently can improve database performance, reduce application processing load, and maintain data consistency across multiple systems.

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Title: MySQL Functions Explained: String, Numeric, User-Defined & Stored Functions

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