牛客网Mysql相应试题 SQL28 计算用户8月每天的练题数量

SQL28 计算用户8月每天的练题数量
描述
题目：现在运营想要计算出2021年8月每天用户练习题目的数量，请取出相应数据。

示例：question_practice_detail

id	device_id	question_id	result	date
1	2138	111	wrong	2021-05-03
2	3214	112	wrong	2021-05-09
3	3214	113	wrong	2021-06-15
4	6543	111	right	2021-08-13
5	2315	115	right	2021-08-13
6	2315	116	right	2021-08-14
7	2315	117	wrong	2021-08-15

根据示例，你的查询应返回以下结果：

day	question_cnt
13	5
14	2
15	3
16	1
18	1

select t.a as day,count(t.device_id)  as question_cnt from

(select day(date) as a,device_id from question_practice_detail where date like '2021-08%') t

group by t.a;

NOW()，用于获取当前日期和时间函数   2024-03-16 10:58:06  select Now()

CURDATE()，用于获取当前日期，同CURRENT_DATE() 2024-03-16

CURTIME()，用于获取当前时间，同CURRENT_TIME() 10:58:06

DATE()函数，用于提取时间字段的日期  2024-03-16

YEAR()函数，用于提取时间字段的年，，返回的格式为"YYYY"

MONTH()函数，用于提取时间字段的月，返回的格式为"mm"，若月份前有0会忽略

DAY()函数，用于提取时间字段的日期，，返回的格式为"dd"，若日期前有0会忽略

TIME()函数，用于提取时间字段的时间，，返回的格式为"HH:ii:ss"

HOUR()函数，用于提取时间字段的小时，，返回的格式为"HH"，若小时前有0会忽略，如08则返回8

MINUTE()函数，用于提取时间字段的分钟，返回的格式为"ii"，若分钟前有0会忽略，如08则返回8

SECOND()函数，用于提取时间字段的秒，返回的格式为"ss"，若秒前有0会忽略，如08则返回8

UNIX_TIMESTAMP()函数，获取当前时间戳，还可以将时间字段转换成时间戳

WEEK()函数    获取日期对应的第几周

QUARTER（）   获取日期对应的季度  

DAYOFYEAR（）  获取当天一日为这一年的第几天

DAYNAME（）   获取对应周几

DAYOFMONTH（）   获取日期是当月的第几天

TIME_TO_SEC（）  获取时间对应的秒

 ADDDATE('2023-05-18 10:58:59',2) 日期加N天

计算两个时间差

 SELECT DATEDIFF('2023-05-31 10:58:59','2023-05-18 10:58:59')

日期减去N天

 SELECT SUBDATE('2023-05-18 10:58:59',2)

--获取当前日期在本周的周一

select subdate(curdate(),date_format(curdate(),'%w')-1) ;

--获取当前日期在本周的周日  

select subdate(curdate(),date_format(curdate(),'%w')-7);

返回：2023-05-21

drop table if exists `user_profile`;
drop table if  exists `question_practice_detail`;
drop table if  exists `question_detail`;
CREATE TABLE `user_profile` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`gender` varchar(14) NOT NULL,
`age` int ,
`university` varchar(32) NOT NULL,
`gpa` float,
`active_days_within_30` int ,
`question_cnt` int ,
`answer_cnt` int 
);
CREATE TABLE `question_practice_detail` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`question_id`int NOT NULL,
`result` varchar(32) NOT NULL,
`date` date NOT NULL
);
CREATE TABLE `question_detail` (
`id` int NOT NULL,
`question_id`int NOT NULL,
`difficult_level` varchar(32) NOT NULL
);

INSERT INTO user_profile VALUES(1,2138,'male',21,'北京大学',3.4,7,2,12);
INSERT INTO user_profile VALUES(2,3214,'male',null,'复旦大学',4.0,15,5,25);
INSERT INTO user_profile VALUES(3,6543,'female',20,'北京大学',3.2,12,3,30);
INSERT INTO user_profile VALUES(4,2315,'female',23,'浙江大学',3.6,5,1,2);
INSERT INTO user_profile VALUES(5,5432,'male',25,'山东大学',3.8,20,15,70);
INSERT INTO user_profile VALUES(6,2131,'male',28,'山东大学',3.3,15,7,13);
INSERT INTO user_profile VALUES(7,4321,'male',28,'复旦大学',3.6,9,6,52);
INSERT INTO question_practice_detail VALUES(1,2138,111,'wrong','2021-05-03');
INSERT INTO question_practice_detail VALUES(2,3214,112,'wrong','2021-05-09');
INSERT INTO question_practice_detail VALUES(3,3214,113,'wrong','2021-06-15');
INSERT INTO question_practice_detail VALUES(4,6543,111,'right','2021-08-13');
INSERT INTO question_practice_detail VALUES(5,2315,115,'right','2021-08-13');
INSERT INTO question_practice_detail VALUES(6,2315,116,'right','2021-08-14');
INSERT INTO question_practice_detail VALUES(7,2315,117,'wrong','2021-08-15');
INSERT INTO question_practice_detail VALUES(8,3214,112,'wrong','2021-05-09');
INSERT INTO question_practice_detail VALUES(9,3214,113,'wrong','2021-08-15');
INSERT INTO question_practice_detail VALUES(10,6543,111,'right','2021-08-13');
INSERT INTO question_practice_detail VALUES(11,2315,115,'right','2021-08-13');
INSERT INTO question_practice_detail VALUES(12,2315,116,'right','2021-08-14');
INSERT INTO question_practice_detail VALUES(13,2315,117,'wrong','2021-08-15');
INSERT INTO question_practice_detail VALUES(14,3214,112,'wrong','2021-08-16');
INSERT INTO question_practice_detail VALUES(15,3214,113,'wrong','2021-08-18');
INSERT INTO question_practice_detail VALUES(16,6543,111,'right','2021-08-13');
INSERT INTO question_detail VALUES(1,111,'hard');
INSERT INTO question_detail VALUES(2,112,'medium');
INSERT INTO question_detail VALUES(3,113,'easy');
INSERT INTO question_detail VALUES(4,115,'easy');
INSERT INTO question_detail VALUES(5,116,'medium');
INSERT INTO question_detail VALUES(6,117,'easy');