How Can I Raise Custom Errors in MySQL Functions?

Raising Errors in MySQL Functions

To ensure data integrity and handle invalid input in MySQL functions, raising errors is essential. In MySQL 5.5 and later, a powerful mechanism known as signals allows developers to create custom error conditions.

Signal Syntax

Signals use the following syntax to raise errors:

SIGNAL SQLSTATE error_code SET MESSAGE_TEXT = 'error_message';

Where:

• error_code: The SQL state error code (e.g., '45000')
• error_message: A custom error message

Example Usage

Consider the following example:

CREATE FUNCTION my_function(a INT, b INT) RETURNS INT
BEGIN
  IF a = 0 OR b = 0 THEN
    SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Invalid input: Zero values not allowed.';
  ELSE
    RETURN a * b;
  END IF;
END;

This function checks if either parameter is equal to zero and raises a custom error if true.

Command Line Demonstration

You can test error handling in the command line client by executing the following statement:

mysql> CALL my_function(0, 5);
ERROR 1644 (45000): Invalid input: Zero values not allowed.

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