sql做题第十一天

第二十四例：链接查询，统计每个用户的平均刷题数

• 题目地址：统计每个用户的平均刷题数牛客题霸牛客网 (nowcoder.com)
  
• 初始化数据

droptable if exists `user_profile`;

droptable if  exists `question_practice_detail`;

CREATETABLE `user_profile` (

`id` intNOTNULL,

`device_id` intNOTNULL,

`gender` varchar(14) NOTNULL,

`age` int ,

`university` varchar(32) NOTNULL,

`gpa` float,

`active_days_within_30` int ,

`question_cnt` int ,

`answer_cnt` int

);

CREATETABLE `question_practice_detail` (

`id` intNOTNULL,

`device_id` intNOTNULL,

`question_id`int NOTNULL,

`result` varchar(32) NOTNULL

);

CREATETABLE `question_detail` (

`id` intNOTNULL,

`question_id`int NOTNULL,

`difficult_level` varchar(32) NOTNULL

);

INSERTINTO user_profile VALUES(1,2138,'male',21,'北京大学',3.4,7,2,12);

INSERTINTO user_profile VALUES(2,3214,'male',null,'复旦大学',4.0,15,5,25);

INSERTINTO user_profile VALUES(3,6543,'female',20,'北京大学',3.2,12,3,30);

INSERTINTO user_profile VALUES(4,2315,'female',23,'浙江大学',3.6,5,1,2);

INSERTINTO user_profile VALUES(5,5432,'male',25,'山东大学',3.8,20,15,70);

INSERTINTO user_profile VALUES(6,2131,'male',28,'山东大学',3.3,15,7,13);

INSERTINTO user_profile VALUES(7,4321,'male',28,'复旦大学',3.6,9,6,52);

INSERTINTO question_practice_detail VALUES(1,2138,111,'wrong');

INSERTINTO question_practice_detail VALUES(2,3214,112,'wrong');

INSERTINTO question_practice_detail VALUES(3,3214,113,'wrong');

INSERTINTO question_practice_detail VALUES(4,6543,111,'right');

INSERTINTO question_practice_detail VALUES(5,2315,115,'right');

INSERTINTO question_practice_detail VALUES(6,2315,116,'right');

INSERTINTO question_practice_detail VALUES(7,2315,117,'wrong');

INSERTINTO question_practice_detail VALUES(8,5432,117,'wrong');

INSERTINTO question_practice_detail VALUES(9,5432,112,'wrong');

INSERTINTO question_practice_detail VALUES(10,2131,113,'right');

INSERTINTO question_practice_detail VALUES(11,5432,113,'wrong');

INSERTINTO question_practice_detail VALUES(12,2315,115,'right');

INSERTINTO question_practice_detail VALUES(13,2315,116,'right');

INSERTINTO question_practice_detail VALUES(14,2315,117,'wrong');

INSERTINTO question_practice_detail VALUES(15,5432,117,'wrong');

INSERTINTO question_practice_detail VALUES(16,5432,112,'wrong');

INSERTINTO question_practice_detail VALUES(17,2131,113,'right');

INSERTINTO question_practice_detail VALUES(18,5432,113,'wrong');

INSERTINTO question_practice_detail VALUES(19,2315,117,'wrong');

INSERTINTO question_practice_detail VALUES(20,5432,117,'wrong');

INSERTINTO question_practice_detail VALUES(21,5432,112,'wrong');

INSERTINTO question_practice_detail VALUES(22,2131,113,'right');

INSERTINTO question_practice_detail VALUES(23,5432,113,'wrong');

INSERTINTO question_detail VALUES(1,111,'hard');

INSERTINTO question_detail VALUES(2,112,'medium');

INSERTINTO question_detail VALUES(3,113,'easy');

INSERTINTO question_detail VALUES(4,115,'easy');

INSERTINTO question_detail VALUES(5,116,'medium');

INSERTINTO question_detail VALUES(6,117,'easy');

• 题目：请你写一个SQL查询，计算山东，不同难度的用户平均答题量，保留四位小数

• 分析1：先找出山东大学的用户：select university from user_profile where university='山东大学'
  
• 分析2：再找出不同难度的用户平均答题量：select university,difficult_level from user_profile u inner join question_practice_detail qpd on u.device_id=qpd.device_id inner join question_detail qd on qod.question_id = qd.question_id where university='山东大学' group by difficult_level;
  
• 分析3：求用户平均答题量：count(qpd.question_id)/count(distinct qpd.device_id)
  

• 示例代码

select

university,

difficult_level,

round(count(qpd.question_id)/count(distinct qpd.device_id),4) as avg_answer_cnt

from

user_profile u

inner join

question_practice_detail qpd

on

u.device_id=qpd.device_id

inner join

question_detail qd

on

qpd.question_id = qd.question_id

where

university='山东大学'

groupby

difficult_level;

第二十五例：组合查询，查找山东大学或者性别为男生的信息

• 查找山东大学或者性别为男生的信息牛客题霸牛客网 (nowcoder.com)
  
• 初始化数据

droptable if exists `user_profile`;

droptable if  exists `question_practice_detail`;

CREATETABLE `user_profile` (

`id` intNOTNULL,

`device_id` intNOTNULL,

`gender` varchar(14) NOTNULL,

`age` int ,

`university` varchar(32) NOTNULL,

`gpa` float,

`active_days_within_30` int ,

`question_cnt` int ,

`answer_cnt` int

);

CREATETABLE `question_practice_detail` (

`id` intNOTNULL,

`device_id` intNOTNULL,

`question_id`int NOTNULL,

`result` varchar(32) NOTNULL

);

CREATETABLE `question_detail` (

`id` intNOTNULL,

`question_id`int NOTNULL,

`difficult_level` varchar(32) NOTNULL

);

INSERTINTO user_profile VALUES(1,2138,'male',21,'北京大学',3.4,7,2,12);

INSERTINTO user_profile VALUES(2,3214,'male',null,'复旦大学',4.0,15,5,25);

INSERTINTO user_profile VALUES(3,6543,'female',20,'北京大学',3.2,12,3,30);

INSERTINTO user_profile VALUES(4,2315,'female',23,'浙江大学',3.6,5,1,2);

INSERTINTO user_profile VALUES(5,5432,'male',25,'山东大学',3.8,20,15,70);

INSERTINTO user_profile VALUES(6,2131,'male',28,'山东大学',3.3,15,7,13);

INSERTINTO user_profile VALUES(7,4321,'male',28,'复旦大学',3.6,9,6,52);

INSERTINTO question_practice_detail VALUES(1,2138,111,'wrong');

INSERTINTO question_practice_detail VALUES(2,3214,112,'wrong');

INSERTINTO question_practice_detail VALUES(3,3214,113,'wrong');

INSERTINTO question_practice_detail VALUES(4,6543,111,'right');

INSERTINTO question_practice_detail VALUES(5,2315,115,'right');

INSERTINTO question_practice_detail VALUES(6,2315,116,'right');

INSERTINTO question_practice_detail VALUES(7,2315,117,'wrong');

INSERTINTO question_practice_detail VALUES(8,5432,117,'wrong');

INSERTINTO question_practice_detail VALUES(9,5432,112,'wrong');

INSERTINTO question_practice_detail VALUES(10,2131,113,'right');

INSERTINTO question_practice_detail VALUES(11,5432,113,'wrong');

INSERTINTO question_practice_detail VALUES(12,2315,115,'right');

INSERTINTO question_practice_detail VALUES(13,2315,116,'right');

INSERTINTO question_practice_detail VALUES(14,2315,117,'wrong');

INSERTINTO question_practice_detail VALUES(15,5432,117,'wrong');

INSERTINTO question_practice_detail VALUES(16,5432,112,'wrong');

INSERTINTO question_practice_detail VALUES(17,2131,113,'right');

INSERTINTO question_practice_detail VALUES(18,5432,113,'wrong');

INSERTINTO question_practice_detail VALUES(19,2315,117,'wrong');

INSERTINTO question_practice_detail VALUES(20,5432,117,'wrong');

INSERTINTO question_practice_detail VALUES(21,5432,112,'wrong');

INSERTINTO question_practice_detail VALUES(22,2131,113,'right');

INSERTINTO question_practice_detail VALUES(23,5432,113,'wrong');

INSERTINTO question_detail VALUES(1,111,'hard');

INSERTINTO question_detail VALUES(2,112,'medium');

INSERTINTO question_detail VALUES(3,113,'easy');

INSERTINTO question_detail VALUES(4,115,'easy');

INSERTINTO question_detail VALUES(5,116,'medium');

INSERTINTO question_detail VALUES(6,117,'easy');

• 题目：分别查看学校为山东大学或者性别为男性的用户的device_id,gender,age,和gap数据，请取出相应结果，不去重

• 分析1：查看学校为山东大学的device_id,gender,age和gpa数据：select device_id,gender,age,gpa from user_file where university='山东大学';
  
• 分析2：性别为男性的用户的device_id,gender,age和gpa数据：select device_id ,gender,age,gpa from user_profile where gender='male';
  
• 需要使用union all把两个查询的数据都输出
  

• 示例代码

select

device_id,gender,age,gpa

from user_profile

where

university='山东大学'

union all

select

device_id,gender,age,gpa

from user_profile

where

gender='male';