SQL - 9
作者:互联网
13.当选者
需求:编写 sql 语句来找到当选者(CandidateId)的名字。
效果展示:
Name |
---|
B |
建表语句:
Create table If Not Exists Candidate (id int, Name varchar(255));
Create table If Not Exists Vote (id int, CandidateId int);
Truncate table Candidate;
insert into Candidate (id, Name) values (1, 'A');
insert into Candidate (id, Name) values (2, 'B');
insert into Candidate (id, Name) values (3, 'C');
insert into Candidate (id, Name) values (4, 'D');
insert into Candidate (id, Name) values (5, 'E');
Truncate table Vote;
insert into Vote (id, CandidateId) values (1, 2);
insert into Vote (id, CandidateId) values (2, 4);
insert into Vote (id, CandidateId) values (3, 3);
insert into Vote (id, CandidateId) values (4, 2);
insert into Vote (id, CandidateId) values (5, 5);
最终SQL:
select
name as "name"
from
Candidate ca
join
(select
CandidateId
from
Vote
group by
CandidateId
order by
count(*) desc
limit 1
) as winner
where ca.id =winer.CandidateId;
14.最高回答率
需求:请编写SQL查询来找到具有最高回答率的问题。
效果展示:
survey_log |
---|
285 |
说明:从 survey_log
表中获得回答率最高的问题,survey_log
表包含这些列:id, action, question_id, answer_id, q_num, timestamp。id 表示用户 id;action 有以下几种值:"show","answer","skip";当 action 值为 "answer" 时 answer_id 非空,而 action 值为 "show" 或者 "skip" 时 answer_id 为空;q_num 表示当前会话中问题的编号。
建表语句:
Create table If Not Exists survey_log (uid int, action varchar(255), question_id int, answer_id int, q_num int, timestamp int);
Truncate table survey_log;
insert into survey_log (uid, action, question_id, answer_id, q_num, timestamp) values (5, 'show', 285, null, 1, 123);
insert into survey_log (uid, action, question_id, answer_id, q_num, timestamp) values (5, 'answer', 285, 124124, 1, 124);
insert into survey_log (uid, action, question_id, answer_id, q_num, timestamp) values (5, 'show', 369, null, 2, 125);
insert into survey_log (uid, action, question_id, answer_id, q_num, timestamp) values (5, 'skip', 369, null, 2, 126);
方法1:
select
question_id as survey_log
from
(select
question_id,
sum(case when action = "answer" then 1 else 0 end) as num_answer,
sum(case when action = "show" then 1 else 0 end )as num_show
from
survey_log
group by
question_id
) as tbkl
order by
(num_answer/num_show) desc
limit 1;
方法2:
select
question_id as "survey_log"
from
survey_log
group by
question_id
order by
count(answer_id) / count(if(action ='show',1,0)) desc
limit 1;
标签:insert,into,values,SQL,answer,survey,id 来源: https://www.cnblogs.com/yuexiuping/p/15159403.html