Insert ó update: Si existe un registro o no existe

[marcosaguileraly]

Amigo, tambien he probado con esto

Código MySQL:

DROP TRIGGER IF EXISTS `promedio`//
CREATE TRIGGER `promedio` AFTER INSERT ON `tabla2`
 FOR EACH ROW BEGIN 
 DECLARE total_final INT(11); 
 -- Cargo la Variable con la Cantidad de Registros  
 SET total_final = (SELECT COUNT(*) FROM final WHERE idalumno= NEW.idalumno GROUP BY idalumno); 
 DECLARE avg INT(11);
  SET avg_alumno = (SELECT AVG(califnum) FROM final WHERE idalumno = NEW.idalumno GROUP BY idalumno);               
-- Luego Tu codigo del If                  
                 
IF total_final = 0 THEN 
     INSERT INTO final (idalumno, califnum) SELECT idalumno, AVG(califnum)  
     as califnum FROM tabla2 WHERE final.idalumno=NEW.idalumno GROUP BY idalumno; 
  END IF; 
    IF total_final > 0 THEN 
     UPDATE final SET 
           final.idalumno= NEW.idalumno, 
           final.califnum= avg_alumno
     WHERE final.idalumno=NEW.idalumno; 
  END IF; 
END
//
 

y no me da resultado!, quiza sea en al sintaxis, me arroja este error:
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE avg INT(11);
SET avg_alumno = (SELECT AVG(califnum) FROM final WHERE ' at line 6