创建数据库
create database;
创建表
create table t1(id int not null auto_increment primary key,
name varchar(20) not null,
age varchar(20) not null,
unique name_age(name,age),
constraint fk_t2_t1 foreign key(name,age) references(name1,age1))engine=innodb default charset=utf8;
create table db1;
delete from db1;只删除内容，不删除序号，后续insert后继续从之前的序号开始递增
truncate table db1;不仅删除内容，同时删除序号，后续insert后从序号1开始递增
drop table t1；
insert into t1(id,name,age) values('s','d',12),('s','d',15)
delete from t1 where id =2
update t1 set name='abc' where age <15
select * from tb1;
select id,name from tb1 where id >5
select id,name from tb1 as a where a.id>5;
通配符：
select name from tb1 where sname like "李%";
分页：
select number from tb1 limit 0,10;
select number from tb1 limit 10 offset 10;从第20行开始取，读取10行
排序：
select * from tb1 order by desc由大到小排序
select * from tb1 order by asc由小到大排序
分组：
select count(id) from tb1 group by id'
聚合函数：
count
max
min
avg
sum等不能使用where作为筛选条件，需要使用having作为筛选条件
连表操作：
select * from tb1 left join tb2 on tb1.name=tb2;
select * from tb1 right join tb2 on tb1.name=tb2
select count(id) from tb2;
navicat使用
备份数据表结构和数据
mysql -u root -p db1>C:\Users\Admin\Desktop\db5.sql
备份数据表结构
mysql -u root -p -d db1>C:\Users\Admin\Desktop\db5.sql
导入：
mysql -u root -p db1<C:\Users\Admin\Desktop\db5.sql
临时表
select corse_id,number from (select * from score where number >=60) as B;