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未完成试卷数大于1的有效用户_牛客题霸_牛客网现有试卷作答记录表exam_record#xff08;uid用户ID, exam_id试卷ID, st。题目来自【牛客题霸】https://www.nowcoder.com/practice/46cb7a33f7204f3ba7f6536d2fc04286?tpId240tqId2183007ru%2…官网链接
未完成试卷数大于1的有效用户_牛客题霸_牛客网现有试卷作答记录表exam_recorduid用户ID, exam_id试卷ID, st。题目来自【牛客题霸】https://www.nowcoder.com/practice/46cb7a33f7204f3ba7f6536d2fc04286?tpId240tqId2183007ru%2Fpractice%2F45a87639110841b6950ef6a12d20175fqru%2Fta%2Fsql-advanced%2Fquestion-rankingsourceUrl
0 问题描述 基于试卷作答记录表exam_record、试卷信息表examination_info 统计2021年每个未完成试卷作答数大于1的有效用户的数据有效用户指完成试卷作答数至少为1且未完成数小于5
1 数据准备
drop table if exists examination_info;
CREATE TABLE examination_info (id int PRIMARY KEY AUTO_INCREMENT COMMENT 自增ID,exam_id int UNIQUE NOT NULL COMMENT 试卷ID,tag varchar(32) COMMENT 类别标签,difficulty varchar(8) COMMENT 难度,duration int NOT NULL COMMENT 时长,release_time datetime COMMENT 发布时间
)CHARACTER SET utf8 COLLATE utf8_general_ci;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 examination_info(exam_id,tag,difficulty,duration,release_time) VALUES(9001, SQL, hard, 60, 2020-01-01 10:00:00),(9002, SQL, easy, 60, 2020-02-01 10:00:00),(9003, 算法, medium, 80, 2020-08-02 10:00:00);INSERT INTO exam_record(uid,exam_id,start_time,submit_time,score) VALUES
(1001, 9001, 2021-07-02 09:01:01, 2021-07-02 09:21:01, 80),
(1002, 9001, 2021-09-05 19:01:01, 2021-09-05 19:40:01, 81),
(1002, 9002, 2021-09-02 12:01:01, null, null),
(1002, 9003, 2021-09-01 12:01:01, null, null),
(1002, 9001, 2021-07-02 19:01:01, 2021-07-02 19:30:01, 82),
(1002, 9002, 2021-07-05 18:01:01, 2021-07-05 18:59:02, 90),
(1003, 9002, 2021-07-06 12:01:01, null, null),
(1003, 9003, 2021-09-07 10:01:01, 2021-09-07 10:31:01, 86),
(1004, 9003, 2021-09-06 12:01:01, null, null),
(1002, 9003, 2021-09-01 12:01:01, 2021-09-01 12:31:01, 81),
(1005, 9001, 2021-09-01 12:01:01, 2021-09-01 12:31:01, 88),
(1005, 9002, 2021-09-01 12:01:01, 2021-09-01 12:31:01, 88),
(1006, 9002, 2021-09-02 12:11:01, 2021-09-02 12:31:01, 89); 2 数据分析
step1: 获取各用户的tag,start_time及未完成标记和已完成标记如果该作答记录交卷了则已完成标记为1未完成标记为0否则相反if(submit_time is null, 1, null) as incomplete
代码如下
select er.uid,ei.tag,er.start_time,-- incomplete 未提交试卷的标记if(er.submit_time is null, 1, null) as incomplete,-- complete已提交试卷的标记if(er.submit_time is not null, 1,null) as complete
from exam_record er
left join examination_info ei on er.exam_id ei.exam_id
where year(er.start_time)2021 step2:
用户分组group by uid统计未完成试卷作答数incomplete_cnt 、已完成试卷作答数complete_cnt_cnt筛选出有效用户having complete_cnt 1 and incomplete_cnt 1 and incomplete_cnt 5 对于每条作答tag用符号 : 来拼接 日期字段和tag字段concat_ws(:, date(start_time), tag); 对于一个人组内的多条作答需去重distinct concat_ws(:, date(start_time), tag); group_concat ( 要连接的字段 [separator 分隔符])
最终代码如下
SELECT uid,-- 未完成试卷的作答数count(incomplete) as incomplete_cnt,-- 已完成试卷的作答数count(complete) as complete_cnt,-- distinct concat_ws(:, date(start_time), tag) as cw-- group_concat ( cw separator ;)group_concat(distinct concat_ws(:, date(start_time), tag) separator ;) as detail
from (SELECT er.uid,ei.tag,er.start_time,-- incomplete 未提交试卷的标记if(er.submit_time is null, 1, null) as incomplete,-- complete已提交试卷的标记if(er.submit_time is not null, 1,null) as completefrom exam_record erleft join examination_info ei on er.exam_id ei.exam_idwhere year(er.start_time)2021
) as t1
group by uid
-- 有效用户完成试卷的作答数至少为1 and 未完试卷的作答数小于5且大于1
having complete_cnt 1 and incomplete_cnt 1 and incomplete_cnt 5
order by incomplete_cnt desc; 3 小结 本案例涉及到if条件判断count即条件聚合。 此外还涉及到date日期函数、concat_ws、group_concat函数的使用 concat_ws(带分隔符的字符串连接函数) 语法concat_ws(string SEP, string A ,string B.......)返回值string说明返回输入字符串连接后的结果,SEP表示各个字符串的分隔符举例select concat_ws(|,ad,cv,op) ;--- ad|cv|op group_concat函数 语法group_concat([distinct] 要连接的字段 [order by 排序字段 asc/desc] [separator 分隔符])说明将group by产生的同一个分组中的值连接起来返回一个字符串结果参数解释distinct排除重复值 如果需要对结果中的值进行排序可以使用order by子句separator 分隔符是拼接符号默认为逗号返回值stringsql举例 #--- 对buyer字段进行分组把去除重复冗余的spending字段的值打印在同一行加号分隔
select buyer,group_concat(distinct spending separator )
from spend
group by buyer;
