Zkuste to, to váš problém jistě vyřeší.
DELIMITER $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `proj_attr`()
BEGIN
DECLARE proj_done, attribute_done BOOLEAN DEFAULT FALSE;
declare attributeId int(11) default 0;
declare projectId int(11) default 0;
DECLARE curProjects CURSOR FOR SELECT id FROM project order by id;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET proj_done = TRUE;
OPEN curProjects;
cur_project_loop: LOOP
FETCH FROM curProjects INTO projectId;
IF proj_done THEN
CLOSE curProjects;
LEAVE cur_project_loop;
END IF;
BLOCK2: BEGIN
DECLARE curAttribute CURSOR FOR SELECT id FROM attribute order by id;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET attribute_done = TRUE;
OPEN curAttribute;
cur_attribute_loop: LOOP
FETCH FROM curAttribute INTO attributeId;
IF proj_done THEN
set proj_done = false;
CLOSE curAttribute;
LEAVE cur_attribute_loop;
END IF;
insert into project_attribute_value(project_id, attribute_id)
values(projectId, attributeId);
END LOOP cur_attribute_loop;
END BLOCK2;
END LOOP cur_project_loop;
END$$
DELIMITER ;