Obrigado! CREATE DEFINER=`root`@`localhost` PROCEDURE `formula`(IN formula VARCHAR(10),IN valor_a FLOAT) 
	BEGIN
 
	SET @s1='SELECT SUM('; 
	SET @s2=CONCAT(@s1,REPLACE(formula,'A','?')); 
	SET @s3=') AS saldo'; 
	SET @s=CONCAT(@s2,@s3);
 
	PREPARE stmt1 FROM @s; 
	SET @a = valor_a; 
	EXECUTE stmt1 USING @a;
 
	DEALLOCATE PREPARE stmt1; 
	    END$$
 
	DELIMITER ;
 
	agora chamando:
 
	CALL formula('A*3/2',2.1);
 
	resultado:
 
	 saldo   
	-------------------- 
	  3.1499998569488525