CREATE FUNCTION - MySQL

Overview

CREATE FUNCTION creates a stored function in the current database for use in SQL statements. Stored functions are used to extend the capabilities of MySQL by creating custom logic that can be reused.

Syntax

CREATE FUNCTION [IF NOT EXISTS] function_name (argument_list) RETURNS return_type AS function_body

Parameters:

  • function_name: The name of the function to be created.
  • argument_list: A comma-separated list of arguments and their data types.
  • RETURNS return_type: The data type of the value returned by the function.
  • function_body: The SQL statement(s) that define the function’s logic.

Options/Flags

  • IF NOT EXISTS: If specified, the function will only be created if it does not already exist.

Examples

Simple Example:

CREATE FUNCTION greet(name VARCHAR(255)) RETURNS VARCHAR(255) AS
RETURN "Hello, " || name || "!";

Example with Multiple Arguments and Return Value:

CREATE FUNCTION calculate_average(num1 INT, num2 INT, num3 INT) RETURNS DECIMAL(10,2) AS
RETURN (num1 + num2 + num3) / 3;

Common Issues

  • Name conflicts: Ensure the function name is unique within the database.
  • Data type mismatch: Check that the data types of the arguments and return value match the declarations.
  • Circular references: Avoid creating functions that reference each other, as this can lead to infinite recursion.

Integration

  • Functions can be called in SQL statements using the following syntax:
SELECT function_name(arguments)
  • Functions can be combined with other MySQL commands, such as SELECT, WHERE, and ORDER BY, to create complex queries.
  • Stored functions can be used to enhance the performance of frequently executed queries.
  • DROP FUNCTION: Removes a stored function from the database.
  • SHOW FUNCTIONS: Displays information about stored functions in the database.
  • MySQL Stored Functions: Official MySQL documentation