ch2-数据管理

2021-11-22 11:30:18 作者：互联网

前言

对数据库的管理是非常重要的,本文基于mysql8.0.

正文

帐号管理

创建新的账号

create user ‘root’@‘localhost’ identified by ‘123456’;
create user ‘root’@‘%’ identified by ‘123456’;

"localhost"是指用户只能在本地登录, 远程登录是 “%”

账号设置新的密码

alter user 'root'@'localhost' identified by '设置的新密码'；

查看账号信息
```
use mysql
select user,host from user;
```
删除账号 drop user ‘账号名’;
用户授权

#语法
GRANT privileges ON databasename.tablename TO 'username'@'host';

#privileges：用户的操作权限，如SELECT，INSERT，UPDATE等，如果要授予所的权限则使用ALL
#databasename：数据库名
#tablename：表名，如果要授予该用户对所有数据库和表的相应操作权限则可用*表示，如*.*

#授予用户指定数据库的指定表的所有权限
grant all privileges on 数据库名.表名 to '用户名'@'主机IP';

#授予用户服务器中所有数据库所有表的所有权限
grant all privileges on *.* to '用户名'@'主机IP';

mysql 新设置用户或更改密码后需用flush privileges刷新MySQL的系统权限相关表，否则会出现拒绝访问

数据库管理

show databases; 显示数据库列表
create database ‘库名’；建立数据库
drop database ‘库名’； 删除数据库
use ‘库名’ ; 接下来操作对该库进行

数据表

show tables; 查看该数据库里的所有表名
create table [表名]（字段名数据类型，-- – ，-- – ）；建立表格
```
mysql> create table account(
-> id int,
-> name varchar(255)
-> );
```
建立表格还可以用检索出来的数据作为数据源
数据类型(有的一定要标明size)
drop table ‘表名’ ； 删除表格
alter table ‘旧表名’ rename ‘新表名’ ； 修改表名
describe ‘表名’ 或 desc ‘表名’ ； 显示数据表的结构,不检索数据
alter table ‘表名’ add ‘字段名’ ‘数据类型’ ‘[not null]’ ‘[default]’ （后俩项为非必要项） 增加一列
```
alter table account add weixin varchar(255);
```
alter table ‘表名’ drop ‘字段名’； 删除一列
alter table ‘表名’ change ‘旧字段名’ ‘新字段名’ ‘数据类型’ ； 修改字段名的信息
```
alter table account change weixin qq varchar(255);
```

数据行

insert into [表名] values(值1,值2,…) ；往表中插入数据( 值个数与字段个数相同)

mysql> desc account;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(255) | YES | | NULL | |
| qq | varchar(255) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
mysql> insert into account(id,
                           name,
                           qq)
    						
values(1,
      'yuwenlong',
      '1589292300');

最好明确指明列,给出列,即使表结构改变,也能继续发生作用, 还有不能插入同一条记录两次

insert into [表名] （列1，列2…) values(值1,值2…) ;只往表中几列插入数据

mysql> select * from account;
+------+-----------+------------+
| id | name | qq |
+------+-----------+------------+
| 1 | yuwenlong | 1589292300 |
+------+-----------+------------+
mysql> insert into account (id,name) values(2,'yyy');
mysql> select * from account;
+------+-----------+------------+
| id | name | qq |
+------+-----------+------------+
| 1 | yuwenlong | 1589292300 |
| 2 | yyy | NULL |
+------+-----------+------------+

update [表名] set [字段名] = xxx [where子句]；修改单列的数据信息，全靠where控制

update [表名] set [字段名1] = xxx ,[字段名2] =xxx … [where子句]；修改多列的数据信息

mysql> alter table account add mm int ;
mysql> select * from account;
+------+-------------+-------------+--------+------+
| id | name | qq | gender | mm |
+------+-------------+-------------+--------+------+
| 1 | yuwenlong | 1589292300 | 1 | NULL |
| 2 | wuchengxiao | 12345678 | 1 | NULL |
| 3 | genziyue | 987654321 | 0 | NULL |
| 3 | zhl | 123213123 | 0 | NULL |
| 4 | zhouyang | 37427837847 | 1 | NULL |
| 5 | ssss | 36261736 | 0 | NULL |
| 6 | erw | 762377278 | 0 | NULL |
| 7 | hsdhf | 3728338 | 1 | NULL |
| 8 | sdfsd | 32477278 | 1 | NULL |
| 9 | jsjdsj | 378282832 | 0 | NULL |
| 10 | sdfs3we | 273878278 | 0 | NULL |
| 11 | ehjrh32 | 636467 | 0 | NULL |
| 12 | 3jjsjd | 37274728372 | 1 | NULL |
| 13 | eyrwyu | 2367476237 | 1 | NULL |
+------+-------------+-------------+--------+------+
mysql> update account 
		set mm = 1 
		where gender=0;
mysql> update account 
		set mm =737 
		where id>=6;
mysql> select * from account ;
+------+-------------+-------------+--------+------+
| id | name | qq | gender | mm |
+------+-------------+-------------+--------+------+
| 1 | yuwenlong | 1589292300 | 1 | NULL |
| 2 | wuchengxiao | 12345678 | 1 | NULL |
| 3 | genziyue | 987654321 | 0 | 1 |
| 3 | zhl | 123213123 | 0 | 1 |
| 4 | zhouyang | 37427837847 | 1 | NULL |
| 5 | ssss | 36261736 | 0 | 1 |
| 6 | erw | 762377278 | 0 | 737 |
| 7 | hsdhf | 3728338 | 1 | 737 |
| 8 | sdfsd | 32477278 | 1 | 737 |
| 9 | jsjdsj | 378282832 | 0 | 737 |
| 10 | sdfs3we | 273878278 | 0 | 737 |
| 11 | ehjrh32 | 636467 | 0 | 737 |
| 12 | 3jjsjd | 37274728372 | 1 | 737 |
| 13 | eyrwyu | 2367476237 | 1 | 737 |
+------+-------------+-------------+--------+------+
mysql> update account 
		set mm =33 
		where mm is NULL;
mysql> select * from account;
+------+-------------+-------------+--------+------+
| id | name | qq | gender | mm |
+------+-------------+-------------+--------+------+
| 1 | yuwenlong | 1589292300 | 1 | 33 |
| 2 | wuchengxiao | 12345678 | 1 | 33 |
| 3 | genziyue | 987654321 | 0 | 1 |
| 3 | zhl | 123213123 | 0 | 1 |
| 4 | zhouyang | 37427837847 | 1 | 33 |
| 5 | ssss | 36261736 | 0 | 1 |
| 6 | erw | 762377278 | 0 | 737 |
| 7 | hsdhf | 3728338 | 1 | 737 |
| 8 | sdfsd | 32477278 | 1 | 737 |
| 9 | jsjdsj | 378282832 | 0 | 737 |
| 10 | sdfs3we | 273878278 | 0 | 737 |
| 11 | ehjrh32 | 636467 | 0 | 737 |
| 12 | 3jjsjd | 37274728372 | 1 | 737 |
| 13 | eyrwyu | 2367476237 | 1 | 737 |
+------+-------------+-------------+--------+------+

插入和更新可以用检索出来的数据作为数据源(子查询)

delete from [表名] [where语句] 从 MySQL 数据表中删除数据

mysql> select * from book2;
+------+---------+---------+-------+
| id | title | content | pages |
+------+---------+---------+-------+
| 1 | dfsd | fdsdf | 23 |
| 2 | sdfdsz | dhfhjsd | 12 |
| 3 | sjhdfj | shjdfhj | 29 |
| 4 | hgdfh | hwsdh | 45 |
| NULL | fdsdf | NULL | NULL |
| NULL | dhfhjsd | NULL | NULL |
| NULL | shjdfhj | NULL | NULL |
| NULL | hwsdh | NULL | NULL |
+------+---------+---------+-------+
mysql> delete from book2 where id is NULL;
Query OK, 4 rows affected (0.02 sec)
mysql> select * from book2;
+------+--------+---------+-------+
| id | title | content | pages |
+------+--------+---------+-------+
| 1 | dfsd | fdsdf | 23 |
| 2 | sdfdsz | dhfhjsd | 12 |
| 3 | sjhdfj | shjdfhj | 29 |
| 4 | hgdfh | hwsdh | 45 |
+------+--------+---------+-------+
mysql> delete from book2 ;
Query OK, 4 rows affected (0.01 sec)
mysql> select * from book2;
Empty set (0.00 sec)

尾言

本文章以便之后个人查阅.

标签：account,mysql,ch2,数据管理,737,表名,NULL,id
来源： https://blog.csdn.net/weixin_42755533/article/details/121468130