数据库
作者：互联网
drop database db1;
create database db1 default charset utf8;
create table t2(id int null,name char(10) not null) engine=innodb default charset=utf8;事务 原子性操作 回滚
create table t3(id int auto_increment primary key,name char(10) not null) engine=innodb default charset=utf8;
primary key 约束 不能空，不能重复 加速查找
一个表里只能有一个自增列和主键
delete from t1；清空表 再插入继续自增
truncate table t1；再插入从1自增 效率快
drop table t1；删除表
数字
tinyint
int
bigint
小数用decimal 精确
num decimal（10，5）总位数和小数点后位数
字符串
char（10）未占满填充 速度快 限制均是255字符
varchar（10）节省空间
text多字符
sql优化：定长放在前，变长放在后
文件，图片，视频存硬盘，数据库存路径
时间类型
date
time
datetime
枚举
create table shirts（
name char（20），
size ENUM（‘small’，‘midium’，‘large’））； 选其一插入
insert into shirts（name，size）values（‘a’，‘large’） ；
集合
create table myset（
name char（20），
col SET（‘a’，‘b’，‘c’））；选任意组合插入
insert into myset（name，col）values（‘a’，‘a，b’） ；
增
insert into tb11(name,age) values('alex',12);
insert into tb11(name,age) values('alex',12),('root',18);
insert into tb12(name,age) select name,age from tb11;
删
delete from tb12;
delete from tb12 where id !=2;
delete from tb12 where id =2 ;
delete from tb12 where id > 2 ;
delete from tb12 where id >=2;
delete from tb12 where id >=2 or name='alex';
改
update tb12 set name='alex' where id>12 and name='xx';
update tb12 set name='alex',age=19 where id>12 and name='xx';
查
select * from tb12;
select id,name from tb12;
select id,name from tb12 where id > 10 or name ='xxx';
select id,name as cname from tb12 where id > 10 or name ='xxx';
select name,age,11 from tb12;
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%";以a开头
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; 从10开始看10条
select * from tb12 limit 20,10;
select * from tb12 limit 10 offset 20;
从第20行开始读取，读取10行；
结合Python分页：
# 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; 先按age排序，如果重复，再按照id排
取后10条数据
select * from tb12 order by id desc limit 10;
外键 节省空间 约束（保证表与表之间数据一致性）
CREATE TABLE t5 (
nid int(11) NOT NULL AUTO_INCREMENT,
pid int(11) not NULL,
num int(11),
primary key(nid,pid)
) 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 t5(nid,pid)
)engine=innodb default charset=utf8;
desc t5;
show create table t5;看表是怎么创建的（sql语句）
show create table t5 \G；竖着看
alter table t5 set AUTO_INCREMENT=1;设置自增起始值
MySQL 步长，基于会话
sqlserver 基于表
show session variables like 'auto_inc%';查看步长
set session auto_increment_increment=2;设置步长
show global variables like 'auto_inc%';查看全局步长
set global auto_increment_increment=2;不推荐
唯一：
约束不能重复（可以为空）
PS: 主键不能重复（不能为空）
加速查找
create table t1(
id int ....,
num int,
xx int,
unique 唯一索引名称 (列名,列名), 联合唯一，两列间不能重复
constraint ....
)
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;
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
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;
分组：
select count(id),max(id),part_id from userinfo5 group by part_id;通过part_id进行分组，返回部门id一样的人数和部门id一样的人中id最大的那一个
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) as count,part_id from userinfo5 group by part_id having count(id) > 1;
连表操作：
select * from userinfo5,department5 where userinfo5.part_id = department5.id;
select * from userinfo5 left join department5 on userinfo5.part_id = department5.id; 推荐使用
# userinfo5左边全部显示
select * from department5 left join userinfo5 on userinfo5.part_id = department5.id;
select * from userinfo5 right join department5 on userinfo5.part_id = department5.id;
# department5右边全部显示
#备份数据表结构+数据：mysqldump -u root db1 > db1.sql -p;转储数据库，备份，防黑客
#备份数据表结构：mysqldump -u root -d db1 > db1.sql -p;
import pymysql
cid=input('>>>')
user=input('>>>')
conn=pymysql.connect(host='localhost',user='root',password='',database='day61')
cursor=conn.cursor() #游标，拿数据
sql="select * from app01_userinfo where id='%s'and name='%s'"%(cid,user) #不要自己写，会有sql注入 1" o r 1=1 --
cursor.execute(sql)
result=cursor.fetchone() #只显示一条
print(result)
cursor.close()
conn.close()
if result:
print('登陆成功')
else:
print('登陆失败')
import pymysql
cid=input('>>>')
user=input('>>>')
conn=pymysql.connect(host='localhost',user='root',password='',database='day61')
cursor=conn.cursor() #游标，拿数据
sql="select * from app01_userinfo where id=%(c)s and name=%(u)s"
#cursor.execute(sql,[cid,user])
cursor.execute(sql,{'c':cid,'u':user})
result=cursor.fetchone() #只显示一条
print(result)
cursor.close()
conn.close()
if result:
print('登陆成功')
else:
print('登陆失败')
正确的写法，防注入
import pymysql
cid=input('>>>')
user=input('>>>')
conn=pymysql.connect(host='localhost',user='root',password='',database='day61')
cursor=conn.cursor() #游标，拿数据
sql="insert into app01_userinfo (id,name) values (%s,%s)"
cursor.execute(sql,(cid,user))
conn.commit()
cursor.close()
conn.close()
#增删改都要commit
r=cursor.executemany(sql,[('',''),('',''),('','')]) #提交多个
r是一个返回值，受影响的行数
import pymysql conn=pymysql.connect(host='localhost',user='root',password='',database='day61') cursor=conn.cursor(cursor=pymysql.cursors.DictCursor) #游标，拿数据 sql="select * from app01_userinfo limit 3" cursor.execute(sql) ''' result=cursor.fetchone() print(result) result=cursor.fetchone() print(result) result=cursor.fetchone() print(result) #cursor.scroll(1,mode='relative') cursor.scroll(2,mode='absolute') result=cursor.fetchone() print(result) result=cursor.fetchone() print(result) ''' result=cursor.fetchall() print(result) cursor.close() conn.close()
标签：10,name,数据库,cursor,tb12,id,select 来源： https://www.cnblogs.com/qwer-123/p/12001732.html