创建数据库
create database db1;
删除数据库
drop database db1;
创建数据表
create table tb1用户表( id int not null auto_increment primary key, name char(10), department_id int, p_id int, )engine=innodb default charset=utf8;
主键（primary key）一个表只能有一个主键，主键可以由一列或者多列组成
外键的创建
CREATE TABLE t5 ( nid int(11) NOT NULL AUTO_INCREMENT, pid int(11) not NULL, num int(11), primary key(nid,pid) --这里就是把两列设置成了主键 ) ENGINE=InnoDB DEFAULT CHARSET=utf8; create table t6( id int auto_increment primary key, name char(10), id1 int, id2 int, CONSTRAINT fk_t5_t6 foreign key (id1,id2) REFERENCES t1(nid,pid) --这里是设置外键 )engine=innodb default charset=utf8;
数据行的操作
数据的插入
insert into tb1(name,age) values('ax',8);
insert into tb12(name,age) select name,age from tb11;表中的数据的删除
delete from t1; truncate table t1; drop table t1 delete from tb1 where id > 10 delete from tb12 where id >=2 or name='alex'
数据的更新
update tb1 set name='root' where id > 10
数据的查询
select * from tb; select id,name from tb;
表结构的查看
show create table t1; desc t1;
其他
select * from tb12 where id != 1 select * from tb12 where id in (1,5,12); select * from tb12 where id not in (1,5,12); select * from tb12 where id in (select id from tb11) select * from tb12 where id between 5 and 12;
通配符
select * from tb12 where name like "a%" select * from tb12 where name like "a_"
分页
select * from tb12 limit 10; select * from tb12 limit 0,10; select * from tb12 limit 10,10; select * from tb12 limit 20,10; select * from tb12 limit 10 offset 20;
# page = input('请输入要查看的页码')
# page = int(page)
# (page-1) * 10
# select * from tb12 limit 0,10; 1
# select * from tb12 limit 10,10;2排序
select * from tb12 order by id desc; 大到小 select * from tb12 order by id asc; 小到大 select * from tb12 order by age desc,id desc;
取后10条数据
select * from tb12 order by id desc limit 10;
分组
select count(id),max(id),part_id from userinfo5 group by part_id;
聚合函数有下面几个：
count max min sum avg
**** 如果对于聚合函数结果进行二次筛选时？必须使用having ****
select count(id),part_id from userinfo5 group by part_id having count(id) > 1; select count(id),part_id from userinfo5 where id > 0 group by part_id having count(id) > 1;
自增值设置
表自增值的设置
alter table t1 auto_increment=20;
-- 这个就表示从开始20开始算，用上面的show create table t1\G 就可以看到当前的值是多少。
基于会话级别
-- 查看当前的会话值
show session variables like 'auto_incre%'
-- 设置会话步长
set session auto_increment_increment=2;
-- 设置起始值
set session auto_increment_offset=10;
基于全局设置
-- 查看全局的设置值
show global variables like 'auto_inc%';
-- 设置全局步长值
set global auto_increment_increment=3;
-- 设置起始值
set global auto_increment_offset=11;
sql server 是在创建表的时候就可以自己设置，灵活度很高
REATE TABLE t5 (nid int(11) NOT NULL AUTO_INCREMENT,pid int(11) NOT NULL,num int(11) DEFAULT NULL,PRIMARY KEY (nid,pid)) ENGINE=InnoDB AUTO_INCREMENT=4, 步长=2 DEFAULT CHARSET=utf8
CREATE TABLE `t6` (
nid int(11) NOT NULL AUTO_INCREMENT,pid int(11) NOT NULL,num int(11) DEFAULT NULL,PRIMARY KEY (nid,pid)) ENGINE=InnoDB AUTO_INCREMENT=4, 步长=20 DEFAULT CHARSET=utf8
唯一索引
create table t1( id int, num int, xx int, unique qu1 (num ,xx) -- 意思就是这两列在一行上面数据不能相同，例如都是1,1,就不行 );
唯一索引：约束不能重复（可以为空）主键索引：约束不能重复（不可以为空）他们的特点都是加速查询
外键一对一
create table userinfo1( id int auto_increment primary key, name char(10), gender char(10), email varchar(64) )engine=innodb default charset=utf8; create table admin( id int not null auto_increment primary key, username varchar(64) not null, password VARCHAR(64) not null, user_id int not null, unique uq_u1 (user_id), CONSTRAINT fk_admin_u1 FOREIGN key (user_id) REFERENCES userinfo1(id) )engine=innodb default charset=utf8;
外键多对多
示例1： 用户表 相亲表 示例2： 用户表 主机表 用户主机关系表 ===》多对多
create table userinfo2( id int auto_increment primary key, name char(10), gender char(10), email varchar(64) )engine=innodb default charset=utf8; create table host( id int auto_increment primary key, hostname char(64) )engine=innodb default charset=utf8; create table user2host( id int auto_increment primary key, userid int not null, hostid int not null, unique uq_user_host (userid,hostid), CONSTRAINT fk_u2h_user FOREIGN key (userid) REFERENCES userinfo2(id), CONSTRAINT fk_u2h_host FOREIGN key (hostid) REFERENCES host(id) )engine=innodb default charset=utf8;
连表操作
select * from userinfo5,department5 select * from userinfo5,department5 where userinfo5.part_id = department5.id select * from userinfo5 left join department5 on userinfo5.part_id = department5.id select * from department5 left join userinfo5 on userinfo5.part_id = department5.id # userinfo5左边全部显示 # select * from userinfo5 right join department5 on userinfo5.part_id = department5.id # department5右边全部显示 select * from userinfo5 innder join department5 on userinfo5.part_id = department5.id 将出现null时一行隐藏 select * from department5 left join userinfo5 on userinfo5.part_id = department5.id left join userinfo6 on userinfo5.part_id = department5.id select score.sid, student.sid from score left join student on score.student_id = student.sid left join course on score.course_id = course.cid left join class on student.class_id = class.cid left join teacher on course.teacher_id=teacher.ti select count(id) from userinfo5;
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