MySQL常用语法

显示有哪些数据库：show databases;

创建数据库：create database database1;

删除数据库：drop database database1;

使用数据库：use database1;

查看表：show tables;

新建表：create table table1(

id int(10) not null primary key auto increment ,

a varchar(20),

b int(10),

c varchar(10) default '男',

d int(10)

);

查看表结构:desc student;

删除表:drop table student;

删除主键:alter table table1 drop primary key;

增加主键:alter table table1 add primary key(id);

删除字段:alter table table1 drop classid;

增加字段:alter table table1 add classid int(10);

增加记录:insert into table1(a,b,c,d) values('哈哈',1,'你好',2);

删除：delete from table1 where b = 1;

修改:update table1 set a = '哈哈哈' where b=1;

通配符 %:多个任意的字符 _:一个字符

update table1 set b = 2 where name like '%i%';

查询:

select * from table1;

select id,name from table1;

select * from table1 where b like '%i%';

排序 默认升序asc 降序desc

select * from table1 order by a asc;

select * from table1 order by a desc;

select * from table1 order by a desc,b asc;

组函数 min max count avg

select count(*) from table1;

select min(a) from table1;

select avg(a) from table1;

select max(a) from table1;

分组:select classid,avg(b) from table1 group by classid having avg(b)>5;

字句作为查询的条件:select * from table1 where age = (select min(b) from table1);

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