auto_increment 自动增长 整形才能做自动增长
NOT NULL 不能为空
DEFAULT 0 默认值为0
PRIMARY KEY 定义主键
ALTER TABLE 修改表
ADD[COLUMN] 增加列
AFTER 在什么之后
CHANGE [COLUMN]
修改表中列名和数据类型
alter table tb2
change column tb2_id tb_id int;
ALTER[COLUMN] 修改和删除默认值；
set 关键词
MODIFY 修改数据类型，修改一个类型
DROP[column] 删除表中列
RENAME[TO] 为表重命名
RENAME TABLE 旧表名 to 新表名
DROP TABLE 删除表
show columns from mysql_test.customers; 查看表列 (显示表的结1
创建双普通索引 方法1;
create index index_cust
on mysql_test.customers(cust_name,sex);
创建升序索引 方法2；add增加 asc升序
alter table mysql_test.class
add index index_stu_name(class_name(3) asc);
查看索引
show index from mysql_test.class;
删除索引
drop index index_stu_name mysql_test.class;
插入语句 方法1
insert into mysql_test.customers
values('xiaoqh',2022,'P','shenzhen','longhua');
插入语句 方法2
insert into mysql_test.customers
set cust_name='chenhq',cust_address='qinghu';
删除语句
DELETE FROM mysql_test.customers
WHERE cust_name=' zenghr';
更新语句
update mysql_test.customers
set cust_address='wuhan'
where cust_name='zenghr';
查询语句
select * from customers; 查询表所有内容
-----------------------------------------------------------
select cust_name,cust_city
from mysql_test.customers; 查询姓名和城市的信息
----------------------------------------------------------
查询换别名
SELECT cust_name as xiangming , cust_city as dizhi
FROM mysql_test.customers;
交叉连接&笛卡尔积
select * from tb1,tb2; 方法1
select * from tb1 cross join tb2; 方法2
两表相连&内连接 必须有相同外码
select *
from tb1 inner join tb2
on tb1.tb_id=tb2.tb2_id;
where子句&条件查询
select * from tb2
where tb2_id=3;
范围查询
select * from customers
where cust_id between 2 and 3;
枚举查询
select * from customers
where cust_id in(1,2);
查询谁的cust_address为null
select cust_name from customers
where cust_address is null;
查看相同地址的人数
select cust_name,sex,count(*) as 'renshu'
from customers
group by cust_address,sex;
查询降序和升序 desc&asc
select cust_id,sex
from customers
order by cust_id desc,sex desc;
限制语句 LIMIT
select cust_id,cust_name
from customers
order by cust_id
limit 2,4;
三表连查
mysql> select b_name,bo_jdate
-> from book,borrow,readers
-> where b_name='yuwen' and readers.re_id=borrow.r_id and borrow.b_id=book.b_id;
最高，最低，平均值 聚合函数 group by
mysql> select b_press,max(b_price),min(b_price),avg(b_price)
-> from book
-> group by b_press;
