create database mydb1;
create database mydb2 charset utf8;
create database mydb3 charset utf8 collate utf8_general_ci
alter database mydb2 charset gbk;
drop database mydb3;
show databases;
show create database mydb1;
use mydb1;
alter database mydb1 charset utf8;
create table employee(
id int primary key auto_increment,
`name` varchar(20) not null,
gender varchar(20),
birthday date,
entry_date date,
job varchar(20),
salary double,
resume text
)
create table employee2(
id int primary key auto_increment,
`name` varchar(20) not null,
gender varchar(20),
birthday date,
entry_date date,
job varchar(20),
salary double,
resume text
)
drop table employee2;
alter table employee add image blob
alter table employee modify job varchar(60)
alter table employee drop gender
rename table employee to `user`
alter table `user` charset utf8
alter table `user` change column `name` username varchar(60)
show tables
show create table `user`
desc `user`
insert into `user`(username) values('zs'),('lisi'),('wangwu')
update `user` set salary=5000
update `user` set salary=3000 where username='zs'
update `user` set salary=4000 and job='ccc' where username='lisi'
update `user` set salary=salary+10000 where username='wangwu'
delete from `user` where username='zs'
delete from `user`
create table exam(
id int primary key auto_increment,
name varchar(20) not null,
chinese double,
math double,
english double
);
insert into exam values(null,'关羽',85,76,70);
insert into exam values(null,'张飞',70,75,70);
insert into exam values(null,'赵云',90,65,95);
insert into exam values(null,'刘备',97,50,50);
insert into exam values(null,'曹操',90,89,80);
insert into exam values(null,'司马懿',90,67,65);
1、查询表中所有学生的信息。
select * from exam;
2、查询表中所有学生的姓名和对应的英语成绩。
select name,english from exam;
3、过滤表中重复数据。
4、在所有学生分数上加10分特长分。
5、统计每个学生的总分。
select *,chinese+math+english from exam;
6、使用别名表示学生分数。
select *,chinese+math+english as 总分 from exam;
7、查询姓名为刘备的学生成绩
select * from exam where name='刘备';
8、查询英语成绩大于90分的同学
select * from exam where english>90;
9、查询总分大于200分的所有同学
select * from exam where chinese+math+english>200;
10、查询英语分数在 80-90之间的同学。
select * from exam where english between 80 and 90;
select * from exam where english>=80 and english<=90;
11、查询数学分数为89,75,91的同学。
select * from exam where math=89 or math=75 or math=91;
select * from exam where math in(89,75,91);
12、查询所有姓刘的学生成绩。
select * from exam where name like '刘%';
13、查询所有姓刘两个字的学生成绩。
select * from exam where name like '刘_';
14、查询数学分>80并且语文分>80的同学。
select * from exam where math>80 and chinese>80;
15、查询数学分>80 或者 语文分>80的同学。
select * from exam where math>80 or chinese>80;
16、对数学成绩排序后输出。
select * from exam order by math;
17、对总分排序按从高到低的顺序输出
select *,chinese+math+english as 总分 from exam order by 总分 desc;
select *,chinese+math+english as 总分 from exam order by chinese+math+
english desc;
18、对姓刘的学生成绩排序输出
select * from exam where name like '刘%' order by math desc;
19、统计一个班级共有多少学生?
select count(id) from exam;
20、统计数学成绩大于或等于90的学生有多少个?
select count(math) from exam where math>=90;
21、统计总分大于250的人数有多少?
select count(id) from exam where chinese+math+english>250;
22、统计一个班级数学总成绩?
selcet * from exam;
23、统计一个班级语文、英语、数学各科的总成绩
select sum(chinese),sum(math),sum(english) from exam;
24、统计一个班级语文、英语、数学的成绩总和
select sum(chinese)+sum(math)+sum(english) from exam;
25、统计一个班级语文成绩平均分
select sum(chinese)/count(id) from exam;
26、求一个班级数学平均分?
select avg(math) from exam;
27、求一个班级总分平均分
select avg(ifnull(chinese,0))+avg(ifnull(math,0))+avg(ifnull(english,0))
from exam;
28、求班级最高分和最低分(数值范围在统计中特别有用)
select max(ifnull(chinese,0)+ifnull(math,0)+ifnull(english,0)) from exam;
select min(ifnull(chinese,0)+ifnull(math,0)+ifnull(english,0)) from exam;
create table orders(
id int,
product varchar(20),
price float
);
insert into orders(id,product,price) values(1,'电视',900);
insert into orders(id,product,price) values(2,'洗衣机',100);
insert into orders(id,product,price) values(3,'洗衣粉',90);
insert into orders(id,product,price) values(4,'桔子',9);
insert into orders(id,product,price) values(5,'洗衣粉',90);
29、查询购买了几类商品,并且每类总价大于100的商品
select product,sum(price) from orders where price>100 group by product;