给下面的代码纠错：create procedure student_score_by_name(in v_sname varchar(20)) begin declare v_sno,v_cno varchar(20); declare v_grade int; declare v_level varchar(10); declare flag int default 1; declare c1 cursor for select sc.sno,cno,grade, level from student,sc where student.sno=sc.sno and sname=v_sname; declare continue handler for not found set flag=0; open c1; while flag do fetch c1 into v_sno,v_cno,v_grade,v_level; if isnull(v_level) then if v_grade between 85 and 100 then set level='A'; elseif v_grade between 75 and 84 then set level='B'; elseif v_grade between 65 and 74 then set level='C'; elseif v_grade between 60 and 64 then set level='D'; else set level='F'; end if; update sc set level=v_level where sno=v_sno and cno=v_cno; end if; end while; close c1; end;

下面是已经纠错的代码：

CREATE PROCEDURE student_score_by_name(in v_sname varchar(20))  
BEGIN 
    DECLARE v_sno, v_cno varchar(20); 
    DECLARE v_grade int; 
    DECLARE v_level varchar(10); 
    DECLARE flag int default 1; 
    DECLARE c1 CURSOR FOR SELECT sc.sno, cno, grade, level FROM student, sc 
        WHERE student.sno = sc.sno AND sname = v_sname; 
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET flag = 0; 
    OPEN c1; 
    WHILE flag DO 
        FETCH c1 INTO v_sno, v_cno, v_grade, v_level; 
        IF isnull(v_level) THEN 
            IF v_grade BETWEEN 85 AND 100 THEN SET v_level = 'A'; 
            ELSEIF v_grade BETWEEN 75 AND 84 THEN SET v_level = 'B'; 
            ELSEIF v_grade BETWEEN 65 AND 74 THEN SET v_level = 'C'; 
            ELSEIF v_grade BETWEEN 60 AND 64 THEN SET v_level = 'D'; 
            ELSE SET v_level = 'F'; 
            END IF; 
            UPDATE sc SET level = v_level WHERE sno = v_sno AND cno = v_cno; 
        END IF; 
    END WHILE; 
    CLOSE c1; 
END;

主要的问题是：

1. 缺少 BEGIN 和 END，需要在创建存储过程时加上。

2. CURSOR 声明语句中 SELECT 语句缺少表别名。

3. isnull() 函数应该写成 IS NULL。

4. 在 IF 语句中，变量名应该是 v_level，而不是 level。

5. 在 END IF 和 END WHILE 后面需要加上分号。