错误1248：每个派生表必须具有自己的别名

Question

请参阅下面的code。我收到错误：

  

错误1248：每个派生表必须有自己的别名

我做错了什么？

CREATE PROCEDURE `insert_seance` (IN compared_id INT)
BLOCK1: BEGIN
    CREATE TEMPORARY TABLE log
    LIKE seance_log;
    CREATE TEMPORARY TABLE compared_log
    LIKE seance_log;
BLOCK2: BEGIN
    DECLARE done, inner_done BOOLEAN DEFAULT FALSE;
    DECLARE diff BOOL DEFAULT TRUE;
    DECLARE current_id, se_id, q_id, ans INT;
    DECLARE compared CURSOR FOR
        SELECT seance_id, question_id, answer FROM seance_log
        WHERE seance_id = compared_id;
    DECLARE seance CURSOR FOR
        SELECT seance_id FROM seances
        WHERE seance_id <> compared_id;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

    OPEN compared;
    WHILE NOT done DO
        FETCH compared INTO se_id, q_id, ans;
        INSERT INTO compared_log (seance_id, question_id, answer)
            VALUES (se_id, q_id, ans);
    END WHILE;
    CLOSE compared;
    SET done = FALSE;

    OPEN seance;
    WHILE NOT done DO
        FETCH seance INTO current_id;
        DELETE FROM log;
        BLOCK3: BEGIN
            DECLARE answers CURSOR FOR
                SELECT seance_id, question_id, answer FROM seance_log
                WHERE seance_id = current_id;
            DECLARE CONTINUE HANDLER FOR NOT FOUND SET inner_done = TRUE;
            DELETE FROM log;
            OPEN answers;
            WHILE NOT inner_done DO
                FETCH answers INTO se_id, q_id, ans;
                INSERT INTO log (seance_id, question_id, answer)
                    VALUES (se_id, q_id, ans);
            END WHILE;
            CLOSE answers;
            SELECT IF ((SELECT COUNT(*) FROM (SELECT 'log' AS `set`, l.*
                FROM log l
                WHERE ROW(l.seance_id, l.question_id, l.answer) NOT IN
                (SELECT * FROM compared_log)
                UNION ALL
                SELECT 'compared_log' AS `set`, cl.*
                FROM compared_log cl
                WHERE ROW(cl.seance_id, cl.question_id, cl.answer) NOT IN
                (SELECT * FROM log)
                )),FALSE,TRUE) INTO diff;
            CASE WHEN diff = FALSE
                THEN DELETE FROM seance_log
                    WHERE seance_id = compared_id;
                UPDATE seances SET count = count + 1
                    WHERE seance_id = compared_id;
            END CASE;
            SET done = NOT diff;
        END BLOCK3;
    END WHILE;
    CLOSE seance;
END BLOCK2;
END BLOCK1