Quick Answer

Handle undefined function calls.

Understanding the Issue

Occurs when calling functions that aren't available in your database version or haven't been created.

The Problem

This code demonstrates the issue:

Sql Error 
SELECT custom_function(); -- If not defined

The Solution

Here's the corrected code:

Sql Fixed 
-- Solution 1: Verify function name
SHOW FUNCTION STATUS;

-- Solution 2: Check database version
SELECT VERSION();

-- Solution 3: Create function if needed
CREATE FUNCTION custom_function() 
RETURNS INT DETERMINISTIC
BEGIN
    RETURN 1;
END;

-- Solution 4: Use equivalent built-in function
-- Example: Use COALESCE instead of IFNULL in some databases

Key Takeaways

Ensure functions exist and are accessible in your database context.