Function execute_create_function 

pub fn execute_create_function(
    stmt: &CreateFunctionStmt,
    db: &mut Database,
) -> Result<(), ExecutorError>

Execute CREATE FUNCTION statement (SQL:1999 Feature P001)

Creates a user-defined function in the database catalog with optional characteristics.

Functions differ from procedures:

• Functions RETURN a value and can be used in expressions
• Functions are read-only (cannot modify database tables)
• Functions only support IN parameters (no OUT/INOUT)
• Functions have recursion depth limiting (max 100 levels)

Characteristics (Phase 6)

• DETERMINISTIC: Indicates same input always produces same output
• SQL SECURITY: DEFINER (default) or INVOKER
• COMMENT: Documentation string
• LANGUAGE: SQL (only supported language)

Examples

Simple function with RETURN expression:

CREATE FUNCTION add_ten(x INT) RETURNS INT
  DETERMINISTIC
  RETURN x + 10;

Complex function with BEGIN…END body:

CREATE FUNCTION factorial(n INT) RETURNS INT
  DETERMINISTIC
  COMMENT 'Calculate factorial of n'
BEGIN
  DECLARE result INT DEFAULT 1;
  DECLARE i INT DEFAULT 2;

  WHILE i <= n DO
    SET result = result * i;
    SET i = i + 1;
  END WHILE;

  RETURN result;
END;

Errors

Returns error if:

• Function name already exists
• Invalid parameter types or return type
• Body parsing fails