MySQL常用操作指令和内置函数，欢迎留言补充！
- 建库，选择库
create database class1824;
use python1804;
- 删库
drop database class1824;
3.建表，删表
create table user(userid int(11),username varchar(32),password char(32));
drop table user;
- 改表名
alter table user rename users;
- 表字段改名
alter table user change userid id int(11);
- 修改字段类型与位置
alter table user modify username char(32) first;
- 添加删除表字段
alter table user add column password char(64) after username;
alter table user drop column sex;
- create创建索引，create 不能创建主键索引，注意与alter的区别
create index in_id on t1(id);
- alter创建索引，create 不能创建主键索引，注意与alter的区别
alter table users add unique(字段名 );
#fulltext(字段名 );primary key(字段名 );index(字段名)
- 删除索引
alter table users drop index username on t1;
- 删除主键索引，先取消递增
alter table users modify id int(11) unsigned not null;
alter table users drop primary key;
- 插入数据方法一，所有字段，顺序一致
insert into users values(1,"haha","adfdsfadsf12"),(2,"xixi","afdsf123321");
- 插入数据方法二，设置了递增的字段可不操作
insert into users(id,username,password) values(3,"hehe","12333adf123");
- 替换列数据
update scores set nu=replace(nu,1,2);
- 去重
select distinct balance from money;
- 排序，desc降序，asc升序。
select * from money where age>30 order by balance desc,age asc limit 2 ,5;
asc升序；
17.分组，group by
select count(province),province from money group by province;
18.条件筛选group by
select count(province) as result,province from money group by province with rollup;
19.条件筛选group by
select count(province) as result,province from money group by province having result>1;
20.表联合查询
select user.username as '用户名',order_goods.oid,order_goods.name as "商品名" from user,order_goods where user.uid=order_goods.uid;
21.表联合查询2
select user.username as '用户',order_goods.name as "商品" from user inner join order_goods on user.uid=order_goods.uid;
22.left join 语法
select * from user left join order_goods on user.uid=order_goods.uid;
23.注意与22的去区别
select * from user where uid in(select uid from order_goods);
select uid from user union all select uid from order_goods;
24.更新数据update
update user set username="哈哈",password="123456" where uid=8;
25.同时对两个表更新
update money m,users u set m.balance=m.balance*u.id,u.password=m.balance where m.id=u.id;
26.delete from，累加id从原来的基础上累加，如1，2，3，将id=2删除了,id=3不变！注意与27中truncate的区别
delete from money where id>9;
delete from 表名；
- truncate清空表以后 id 从1 开始
truncate table users;
28.数据库远程连接,注意符号*的使用
grant 权限 on 库名.表名 to '用户名'@'ip地址' identified by 密码；
grant all on *.* to 'root'@'localhost' identified by '123456' with grant option;
grant select,insert on class1824.* to 'jinxingping'@'localhost' identified by '123321';
flush privileges;
service mysql restart；
29.删除指定权限
revoke insert on class1824.* from 'jinxingping'@'localhost';
30.复制表结构和数据
create table user1 like users；
insert into user1 select * from users；
31.表视图 view
create view v_t1 as select * from t1 where id>2 and id<8; show create/drop view v_t1;
- mysql常用内置函数
mysql 显示内容 用 select
字符串函数
mysql> select concat("hello","world") as nihao; #拼接字符串
select lcase("MYSQL");#转小写
select ucase("mysql"); #转大写
mysql> select length("haha"); 字符串的长度
mysql> select ltrim(" haha"); 去除左侧空格
+-------------------+
| ltrim(" haha") |
+-------------------+
| haha |
+-------------------+
1 row in set (0.00 sec)
mysql> select rtrim(" haha ");去除右侧空格
mysql> select repeat("重要的事情说三遍",6);
select replace("java 是世界上最好的语言","java","python");
mysql> select substr("python is so good",2,7); 从第二个字符开始 截取7个 mysql 从1开始
mysql> select concat(space(20),'haha'); #生成20个空格
数学函数
mysql> select ceiling(123.1);
mysql> select floor(123.1);
mysql> select rand(); 求随机数 0-1之间的小数
mysql> select bin(10);
日期函数
mysql> select curdate(); 返回日期 2018-7-25
mysql> select curtime(); 11:21:33
mysql> select now(); 日期+时间 2018-07-25 11:22:14
mysql> select week(now()); 返回29 表示当前第几周
mysql> select year(now()); 返回2018
mysql> select unix_timestamp(now()); 当前时间的时间戳
mysql> select from_unixtime(1532489069);
+---------------------------+
| from_unixtime(1532489069) |
+---------------------------+
| 2018-07-25 11:24:29 |
+---------------------------+ 将当前的时间戳格式化为日期