DELIMITER $$
CREATE OR REPLACE DEFINER=`vn-admin`@`localhost` FUNCTION `vn`.`testNIF`(vNIF VARCHAR(9))
	RETURNS tinyint(1)
	DETERMINISTIC
BEGIN

	DECLARE vIndice INT;
 	DECLARE vParteNumerica DECIMAL(8,0);
 	DECLARE vLetra VARCHAR(1);
 	DECLARE vLetrasPosibles VARCHAR(24) DEFAULT "TRWAGMYFPDXBNJZSQVHLCKE";
 
    SET vLetra = SUBSTRING(vNIF, 9, 1);
   
   	SET vParteNumerica = CAST(SUBSTRING(vNIF, 1, 8) AS DECIMAL(8,0));
   
    SET vIndice = Round(vParteNumerica MOD 23, 0) + 1;
    
    If SUBSTRING(vLetrasPosibles, vIndice, 1) = vLetra Then
       
        RETURN TRUE;
       
    ELSE
        
		RETURN FALSE;
    
    END IF;
   
END$$
DELIMITER ;