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题解 | #统计作答次数#

分析题目题目条件：三个概念，已完成，未完成，已做答的题目初始提交版本：只利用了字段exam_id select total_pv ,complete_pv,complete_exam_cnt from (select count(exam_id) as total_pv from exam_...

Mysql

2022-04-12

1 393

题解 | #SQL类别高难度试卷得分的截断平均值#

分析题目题目条件： SQL中高难度，所以筛选条件为 where difficulty ='hard' and tag='SQL' 难点1. 截断平均值 (sum(score)-max(score)-min(score))/(count(score)-2) 难点2. 保留一位小数 round（.....

Mysql

2022-04-12

0 317

题解 | #修改表#

alter table user_info add column school varchar(15) after level; alter table user_info change column job profession varchar(10); alter table user_info...

Mysql

2022-04-11

0 282

题解 | #创建一张新表#

create table if not exists user_info_vip( id int primary key auto_increment comment '自增ID', uid int unique not null comment'用户ID', nick_name varchar...

Mysql

2022-04-11

0 287

题解 | #删除记录（三）#

truncate table nowcoder_exam_record #删除表中内容除了用delete 外还有truncate table 表名区别： 1.truncate的速度快，效率高，不能＋where 表示清空表中所有的数据 2.truncate 删除后再插入值时自增长列从1开始，而...

Mysql Mysql

2022-04-07

2 445

题解 | #插入记录（二）#

法一： delete from examination_info where exam_id =9003; insert into examination_info (exam_id ,tag ,difficulty ,duration,release_time ) values(9003,"SQ...

Mysql

2022-03-31

0 285

题解 | #插入记录（二）#

insert into exam_record_before_2021 (uid ,exam_id ,start_time,submit_time,score ) select uid ,exam_id ,start_time,submit_time,score from exam_record...

Mysql

2022-03-31

0 264

题解 | #将两个 SELECT 语句结合起来（一）#

select * from OrderItems where quantity=100 union select * from OrderItems where prod_id like 'BNBG%' order by prod_id #联合查询用于查询多表并且返回结果一致 #通配符like的...

Mysql

2022-03-31

0 248

题解 | #返回顾客名称和相关订单号以及每个订单的总价#

select c.cust_name , t.order_num, t.OrderTotal from Customers c join Orders o on c.cust_id =o.cust_id join (select order_num ,sum( quantity *item_pric...

Mysql

2022-03-29

0 324

题解 | #查找入职员工时间排名倒数第三的员工所有信息#

SELECT * from employees order by hire_date DESC LIMIT 2,1 ---limit表示从第三行取一条数据---order by ＋列名＋desc/asc

Mysql

2021-09-15

1 297