Mysql的使用，常用的SQL语句

一、启动mysql服务

- 启动mysql服务：
systemctl start mysqld.service

• root用户登录mysql：
  
  修改root 密码：
  
  alter user 'root'@'localhost' identified by'new_pwd';

或：

update mysql.user set authentication_string = password('你的密码') where user='root';

flush privileges;

并创建一个普通用户

[root@localhost ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 61
Server version: 5.7.20 MySQL Community Server (GPL)
...................................
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
........................
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> grant all on test.* to 'user'@'localhost' identified by'new_pwd_for_user';
Query OK, 0 rows affected, 1 warning (0.00 sec)

通过命令grant all on test.* to '你的账户名'@'ip' identified by'你的密码';创建创建一个账户，并把test库下所有表，所有权限授权给该账户， IP= localhost 意思只允许本地访问，%意思为允许任何一个地方访问，填写其他ip，就是允许某个远程Ip访问。

二、建库、建表、创数据

1. 查看当前用户下数据库：
show databases;

1. 创建一个新数据库：my_test 并支持中文
   
   create database my_test charset utf8;

2. 转移到该数据库下：use db
   
   use my_test

3. 创建一个表：mytable 两个字段 name register_date
   
   create table mytable(
   
   id int not null auto_increment primary key,
   
   name char(32) not null,
   
   register_date DATE not null);

4. 向表中插入一条数据：insert into id字段已设置为主键自增，不用管
   
   insert into mytable(name, register_date) values('lina', '2018-01-17');

mysql> create database my_test;
Query OK, 1 row affected (0.41 sec)

mysql> use my_test;
Database changed
mysql> create table mytable(
    -> id int not null auto_increment primary key,
    -> name char(32) not null,
    -> register_date DATE not null);
Query OK, 0 rows affected (5.37 sec)

mysql> insert into mytable(name, register_date) values('lina', '2018-01-17');
Query OK, 1 row affected (0.58 sec)

2.2 删库、删表、删数据 （跑路）

• 查询数据：select
  
  select * from table_name; 后面可以加条件语句

• 删数据：delete
  
  delete from tb_name where condition;

如：delete from mytable where id=1 and name='alex' and id>2;

mysql> select * from mytable;
+----+-------+---------------+
| id | name  | register_date |
+----+-------+---------------+
|  1 | lina  | 2018-01-17    |
|  2 | alex  | 2018-08-17    |
|  3 | david | 2015-08-17    |
|  4 | sevn  | 2218-11-17    |
+----+-------+---------------+
4 rows in set (0.14 sec)

mysql> delete from mytable where name='lina' and name='alex';;
Query OK, 2 rows affected (0.29 sec)

mysql> select * from mytable;
+----+-------+---------------+
| id | name  | register_date |
+----+-------+---------------+
|  3 | david | 2015-08-17    |
|  4 | sevn  | 2218-11-17    |
+----+-------+---------------+
2 rows in set (0.00 sec)

mysql> delete from mytable where id>2;

• 删字段：drop
  
  alter table mytable drop column register_date;

• 查看表结构：desc
  
  desc mytable

mysql> alter table mytable drop column register_date;
Query OK, 0 rows affected (2.51 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc mytable;
+-------+----------+------+-----+---------+----------------+
| Field | Type     | Null | Key | Default | Extra          |
+-------+----------+------+-----+---------+----------------+
| id    | int(11)  | NO   | PRI | NULL    | auto_increment |
| name  | char(32) | NO   |     | NULL    |                |
+-------+----------+------+-----+---------+----------------+
2 rows in set (0.22 sec)

• 删表：drop
  
  drop table mytable;

查看库下所有表：show tables;

mysql> drop table mytable;
Query OK, 0 rows affected (0.30 sec)

mysql> show tables;
Empty set (0.04 sec)

• 删库：drop
  
  drop database my_test;

小结：

只有删数据使用：delete

其他所有都用：drop

删库：drop db;

删表：drop tb_name;

删字段：alter table tb_name drop column name;