主页 > 数据库 > MySQL的开发必会的sql语句

MySQL的开发必会的sql语句

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 ,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 ,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;

作者:代码与远方

说点什么吧
  • 全部评论(0
    还没有评论,快来抢沙发吧!