just cannot fetch all content into variables

Question

This is my code, my problem is content of ParentId and Tags is always null. It's not supposed to be like this. I do not why it happens? Can somebody tell why?

CREATE PROCEDURE appendtags() BEGIN DECLARE done INT;
DECLARE postId_1,postId_2,parentId INT(11);

DECLARE tags VARCHAR(128);

DECLARE cur1 CURSOR FOR SELECT PostId,ParentId FROM test.t1;

DECLARE cur2 CURSOR FOR SELECT PostId,Tags FROM test.t2;

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

SET done=0;

OPEN cur1;

OPEN cur2;

REPEAT

IF postId_2=parentId THEN

   INSERT INTO t3 VALUES(postId_1,parentId,tags);

ELSE

   FETCH cur2 INTO postId_2,tags;

END IF;

FETCH cur1 INTO postId_1,ParentId;

UNTIL done END REPEAT;

CLOSE cur1;

CLOSE cur2;

SET done=0;

END