现有试卷作答记录表exam_record（uid用户ID, exam_id试卷ID, start_time开始作答时间, submit_time交卷时间, score得分）： id uid exam_id start_time submit_time score 1 1001 9001 2020-01-01 09:01:01 2020-01-01 09:21:59 90 2 1002 9001 2020-01-20 10:01:01 2020-01-20 10:10:01 89 3 1002 9001 2020-02-01 12:11:01 2020-02-01 12:31:01 83 4 1003 9001 2020-03-01 19:01:01 2020-03-01 19:30:01 75 5 1004 9001 2020-03-01 12:01:01 2020-03-01 12:11:01 60 6 1003 9001 2020-03-01 12:01:01 2020-03-01 12:41:01 90 7 1002 9001 2020-05-02 19:01:01 2020-05-02 19:32:00 90 8 1001 9002 2020-01-02 19:01:01 2020-01-02 19:59:01 69 9 1004 9002 2020-02-02 12:01:01 2020-02-02 12:20:01 99 10 1003 9002 2020-02-02 12:01:01 2020-02-02 12:31:01 68 11 1001 9002 2020-02-02 12:01:01 2020-02-02 12:43:01 81 12 1001 9002 2020-03-02 12:11:01 (NULL) (NULL) 请输出每份试卷每月作答数和截止当月的作答总数。 由示例数据结果输出如下： exam_id start_month month_cnt cum_exam_cnt 9001 202001 2 2 9001 202002 1 3 9001 202003 3 6 9001 202005 1 7 9002 202001 1 1 9002 202002 3 4 9002 202003 1 5 解释：试卷9001在202001、202002、202003、202005共4个月有被作答记录，每个月被作答数分别为2、1、3、1，截止当月累积作答总数为2、3、6、7。
示例1

输入

drop table if exists exam_record;
CREATE TABLE exam_record (
    id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID',
    uid int NOT NULL COMMENT '用户ID',
    exam_id int NOT NULL COMMENT '试卷ID',
    start_time datetime NOT NULL COMMENT '开始时间',
    submit_time datetime COMMENT '提交时间',
    score tinyint COMMENT '得分'
)CHARACTER SET utf8 COLLATE utf8_general_ci;

INSERT INTO exam_record(uid,exam_id,start_time,submit_time,score) VALUES
(1001, 9001, '2020-01-01 09:01:01', '2020-01-01 09:21:59', 90),
(1002, 9001, '2020-01-20 10:01:01', '2020-01-20 10:10:01', 89),
(1002, 9001, '2020-02-01 12:11:01', '2020-02-01 12:31:01', 83),
(1003, 9001, '2020-03-01 19:01:01', '2020-03-01 19:30:01', 75),
(1004, 9001, '2020-03-01 12:01:01', '2020-03-01 12:11:01', 60),
(1003, 9001, '2020-03-01 12:01:01', '2020-03-01 12:41:01', 90),
(1002, 9001, '2020-05-02 19:01:01', '2020-05-02 19:32:00', 90),
(1001, 9002, '2020-01-02 19:01:01', '2020-01-02 19:59:01', 69),
(1004, 9002, '2020-02-02 12:01:01', '2020-02-02 12:20:01', 99),
(1003, 9002, '2020-02-02 12:01:01', '2020-02-02 12:31:01', 68),
(1001, 9002, '2020-02-02 12:01:01', '2020-02-02 12:43:01', 81),
(1001, 9002, '2020-03-02 12:11:01', null, null);

输出

9001|202001|2|2
9001|202002|1|3
9001|202003|3|6
9001|202005|1|7
9002|202001|1|1
9002|202002|3|4
9002|202003|1|5
加载中...