mysql 1280_mysql基础
2.给数据库的root管理员账户设置密码123，再修改成1234
[root@NaNaQi ~]# mysql -uroot
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection idis 10Server version:10.3.11-MariaDB MariaDB Server
Copyright (c)2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type'help;' or '\h' for help. Type '\c'to clear the current input statement.
MariaDB [(none)]> set password = password('123'); #这里的password是加密
Query OK,0 rows affected (0.002sec)
MariaDB [(none)]> Ctrl-C -- exit!Aborted
验证
[root@NaNaQi~]# mysql -uroot -p
Enter password:
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection idis 11Server version:10.3.11-MariaDB MariaDB Server
Copyright (c)2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type'help;' or '\h' for help. Type '\c'to clear the current input statement.
MariaDB [(none)]>修改密码
[root@NaNaQi~]# mysql -uroot -p
Enter password:
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection idis 12Server version:10.3.11-MariaDB MariaDB Server
Copyright (c)2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type'help;' or '\h' for help. Type '\c'to clear the current input statement.
MariaDB [(none)]> alter user root@localhost identified by '1234';
Query OK,0 rows affected (0.001sec)
MariaDB [(none)]>quit
Bye
3.安全初始化数据库，更改root密码为12345
[root@NaNaQi ~]# mysql_secure_installation
NOTE: RUNNING ALL PARTS OF THIS SCRIPT IS RECOMMENDED FOR ALL MariaDB
SERVERS IN PRODUCTION USE! PLEASE READ EACH STEP CAREFULLY!In order to log into MariaDB to secure it, we'll need the current
password for the root user. If you've just installed MariaDB, and
you haven't set the root password yet, the password will be blank,
so you should just press enter here.
Enter current passwordfor root (enter fornone):
OK, successfully used password, moving on...
Setting the root password ensures that nobody can log into the MariaDB
root user without the proper authorisation.
You already have a root passwordset, so you can safely answer 'n'.
Change the root password? [Y/n] y #修改root密码?New password:
Re-enter newpassword:
Password updated successfully!Reloading privilege tables..
... Success!Bydefault, a MariaDB installation has an anonymous user, allowing anyone
to log into MariaDB without having to have a user account createdforthem. Thisis intended only fortesting, and to make the installation
go a bit smoother. You should remove them before moving into a
production environment.
Remove anonymous users? [Y/n] y #删除匿名用户?... Success!Normally, root should only be allowed to connectfrom 'localhost'. This
ensures that someone cannot guess at the root passwordfromthe network.
Disallow root login remotely? [Y/n] n #禁止root远程登录?... skipping.
Bydefault, MariaDB comes with a database named 'test'that anyone can
access. Thisis also intended only fortesting, and should be removed
before moving into a production environment.
Remove test database and access to it? [Y/n] y #删除测试数据库并访问它?
-Dropping test database...
... Success!
-Removing privileges on test database...
... Success!Reloading the privilege tables will ensure that all changes made so far
will take effect immediately.
Reload privilege tables now? [Y/n] y #现在重新加载特权表吗?... Success!Cleaning up...
All done! If you've completed all of the above steps, your MariaDB
installation should now be secure.
Thanksfor using MariaDB!
4.用两种方法查看数据库
MariaDB [(none)]>show databases;+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
+--------------------+
3 rows in set (0.000sec)
MariaDB [(none)]>quit
Bye
[root@NaNaQi~]# mysql -uroot -p12345 -e 'show databases;'
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
+--------------------+
5.创建数据库school之后再删除
MariaDB [(none)]> create database ifnot exists school;
Query OK,0 rows affected, 1 warning (0.000sec)
MariaDB [(none)]>show databases;+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| school |
+--------------------+
4 rows in set (0.000sec)
MariaDB [(none)]> drop database ifexists school;
Query OK,0 rows affected (0.001sec)
MariaDB [(none)]>show databases;+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
+--------------------+
3 rows in set (0.001 sec)
6.创建数据库school，在其里面创建表student，表里面有id，name，age，使用desc命令查看表 student数据。
MariaDB [(none)]>create database school;
Query OK,1 row affected (0.000sec)
MariaDB [(none)]>use school;
Database changed
MariaDB [school]>show tables;
Emptyset (0.000sec)
MariaDB [school]> create table student(id int not null,name varchar(50)null,age tinyint);
Query OK,0 rows affected (0.002sec)
MariaDB [school]>show tables;+------------------+
| Tables_in_school |
+------------------+
| student |
+------------------+
1 row in set (0.000sec)
MariaDB [school]>desc student;+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(50) | YES | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.001 sec)
7.修改表student，插入班级class，之后再删除age一行，最后删除表student。
MariaDB [school]> alter table student add class varchar(20);
Query OK,0 rows affected (0.002sec)
Records:0 Duplicates: 0 Warnings: 0MariaDB [school]>desc student;+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(50) | YES | | NULL | |
| age | tinyint(4) | YES | | NULL | |
| class | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.001sec)
MariaDB [school]>alter table student drop age;
Query OK,0 rows affected (0.005sec)
Records:0 Duplicates: 0 Warnings: 0MariaDB [school]>desc student;+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(50) | YES | | NULL | |
| class | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.001sec)
MariaDB [school]>drop table student;
Query OK,0 rows affected (0.038sec)
MariaDB [school]>show tables;
Emptyset (0.000 sec)
8.授权主机，与192.168.44.129登录数据库的所有数据库与所有表，权限为所有权限，用户为root，密码为12345
MariaDB [school]> grant all on *.* to 'root'@'192.168.27.149' identified by '12345';Query OK, 0 rows affected (0.002sec)
MariaDB [school]> grant all on *.* to 'root'@'192.168.44.129' identified by '12345';
Query OK,0 rows affected (0.001 sec)
9.查看root用户在的192.168.27.149的权限，并取消root用户的192.168.44.129的授权
MariaDB [school]> show grants for 'root'@'192.168.44.129';+-------------------------------------------------------------------------------------------------
| Grants for root@192.168.44.129
+------------------------------------------------------------------------------------------------
| GRANT SELECT, INSERT, UPDATE, CREATE, DROP, RELOAD, SHUTDOWN, PROCESS, FILE, REFERENCES, INDEX, ALTER, SHOW DATABASES, SUPER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, REPLICATION SLAVE, REPLICATION CLIENT, CREATE VIEW, SHOW VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, EVENT, TRIGGER, CREATE TABLESPACE, DELETE VERSIONING ROWS ON *.* TO 'root'@'192.168.44.129' IDENTIFIED BY PASSWORD '*00A51F3F48415C7D4E8908980D443C29C69B60C9' |
+-------------------------------------------------------------------------------------------------
1 row in set (0.000 sec)
10.在school数据库中创建表student，在其中先单次插入一条数据，再连续插入五条数据。表student包含id,name,age。
MariaDB [school]>use school;
Database changed
MariaDB [school]> create table student (id int not null,name varchar(50),age tinyint);
Query OK,0 rows affected (0.039sec)
MariaDB [school]>show tables;+------------------+
| Tables_in_school |
+------------------+
| student |
+------------------+
1 row in set (0.001sec)
MariaDB [school]>desc student;+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(50) | YES | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.001sec)
MariaDB [school]> insert into student values(1,'tom',15);
Query OK,1 row affected (0.001sec)
MariaDB [school]> select * fromstudent;+----+------+------+
| id | name | age |
+----+------+------+
| 1 | tom | 15 |
+----+------+------+
1 row in set (0.001sec)
MariaDB [school]> insert into student values(2,'zhangshan',20),(3,'lisi',18),(4,'wangwu',20),(5,'zhaosan',13),(6,'qianliu',14);
Query OK,5 rows affected (0.001sec)
Records:5 Duplicates: 0 Warnings: 0MariaDB [school]> select * fromstudent;+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 1 | tom | 15 |
| 2 | zhangshan | 20 |
| 3 | lisi | 18 |
| 4 | wangwu | 20 |
| 5 | zhaosan | 13 |
| 6 | qianliu | 14 |
+----+-----------+------+
6 rows in set (0.000 sec)
11.创建表teacher，设置id为主键且自动增长。(只有主键才能设置自动增长)
MariaDB [school]> create table teacher(id int not null primary key auto_increment,name varchar(20) not null,age tinyint,salary float);
Query OK,0 rows affected (0.004sec)
MariaDB [school]>desc teacher;+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| age | tinyint(4) | YES | | NULL | |
| salary | float | YES | | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.001 sec)
12.往表teacher里插入三条数据，再往表teacher里连续插入多条数据。(需指定插入数据的字段)
MariaDB [school]> insert into teacher values(1,'chengsongling',21,4000);
Query OK,1 row affected (0.001sec)
MariaDB [school]> insert into teacher values(2,'chengsongling',21,4000);
Query OK,1 row affected (0.001sec)
MariaDB [school]> insert into teacher values(3,'taochi',21,4000);
Query OK,1 row affected (0.001sec)
MariaDB [school]> select * fromteacher;+----+---------------+------+--------+
| id | name | age | salary |
+----+---------------+------+--------+
| 1 | chengsongling | 21 | 4000 |
| 2 | chengsongling | 21 | 4000 |
| 3 | taochi | 21 | 4000 |
+----+---------------+------+--------+
3 rows in set (0.000sec)
MariaDB [school]> insert into teacher(name,age,salary) values('meijianbiao',30,9000),('mufeng',23,5000),('fangxinxin',24,10000),('leichen',21,10000),('yuqinhao',50,100000),('tanghaolun',10,10000);
Query OK,6 rows affected (0.001sec)
Records:6 Duplicates: 0 Warnings: 0MariaDB [school]> select * fromteacher;+----+---------------+------+--------+
| id | name | age | salary |
+----+---------------+------+--------+
| 1 | chengsongling | 21 | 4000 |
| 2 | chengsongling | 21 | 4000 |
| 3 | taochi | 21 | 4000 |
| 4 | meijianbiao | 30 | 9000 |
| 5 | mufeng | 23 | 5000 |
| 6 | fangxinxin | 24 | 10000 |
| 7 | leichen | 21 | 10000 |
| 8 | yuqinhao | 50 | 100000 |
| 9 | tanghaolun | 10 | 10000 |
+----+---------------+------+--------+
9 rows in set (0.000 sec)
13.修改表teacher中的数据,先把id为9的那行数据年龄改成35，再把年龄改成30，工资改成50000。
MariaDB [school]> update teacher set age = 35 where id = 9;
Query OK,1 row affected (0.001sec)
Rows matched:1 Changed: 1 Warnings: 0MariaDB [school]> select * fromteacher;+----+---------------+------+--------+
| id | name | age | salary |
+----+---------------+------+--------+
| 1 | chengsongling | 21 | 4000 |
| 2 | chengsongling | 21 | 4000 |
| 3 | taochi | 21 | 4000 |
| 4 | meijianbiao | 30 | 9000 |
| 5 | mufeng | 23 | 5000 |
| 6 | fangxinxin | 24 | 10000 |
| 7 | leichen | 21 | 10000 |
| 8 | yuqinhao | 50 | 100000 |
| 9 | tanghaolun | 35 | 10000 |
+----+---------------+------+--------+
9 rows in set (0.001sec)
ariaDB [school]> update teacher set age = 30,salary = 50000 where id = 9;
Query OK,1 row affected (0.003sec)
Rows matched:1 Changed: 1 Warnings: 0MariaDB [school]> select * fromteacher;+----+---------------+------+--------+
| id | name | age | salary |
+----+---------------+------+--------+
| 1 | chengsongling | 21 | 4000 |
| 2 | chengsongling | 21 | 4000 |
| 3 | taochi | 21 | 4000 |
| 4 | meijianbiao | 30 | 9000 |
| 5 | mufeng | 23 | 5000 |
| 6 | fangxinxin | 24 | 10000 |
| 7 | leichen | 21 | 10000 |
| 8 | yuqinhao | 50 | 100000 |
| 9 | tanghaolun | 30 | 50000 |
+----+---------------+------+--------+
9 rows in set (0.001 sec)
14.查找teacher表name与salary一项,再给name设置显示的别名为姓名，给salary设置显示的别名为薪资。
MariaDB [school]> select name,salary fromteacher;+---------------+--------+
| name | salary |
+---------------+--------+
| chengsongling | 4000 |
| chengsongling | 4000 |
| taochi | 4000 |
| meijianbiao | 9000 |
| mufeng | 5000 |
| fangxinxin | 10000 |
| leichen | 10000 |
| yuqinhao | 100000 |
| tanghaolun | 50000 |
+---------------+--------+
9 rows in set (0.001sec)
MariaDB [school]> select name as '姓名',salary as '薪资' fromteacher;+---------------+--------+
| 姓名 | 薪资 |
+---------------+--------+
| chengsongling | 4000 |
| chengsongling | 4000 |
| taochi | 4000 |
| meijianbiao | 9000 |
| mufeng | 5000 |
| fangxinxin | 10000 |
| leichen | 10000 |
| yuqinhao | 100000 |
| tanghaolun | 50000 |
+---------------+--------+
9 rows in set (0.000 sec)
15.先查找薪资为50000的数据的姓名，再查找薪资大于8000的所有记录，最后查找年龄再25到30之间的记录。
MariaDB [school]> select name from teacher where salary = 50000;+------------+
| name |
+------------+
| tanghaolun |
+------------+
1 row in set (0.000sec)
MariaDB [school]> select * from teacher where salary > 8000;+----+-------------+------+--------+
| id | name | age | salary |
+----+-------------+------+--------+
| 4 | meijianbiao | 30 | 9000 |
| 6 | fangxinxin | 24 | 10000 |
| 7 | leichen | 21 | 10000 |
| 8 | yuqinhao | 50 | 100000 |
| 9 | tanghaolun | 30 | 50000 |
+----+-------------+------+--------+
5 rows in set (0.001sec)
MariaDB [school]> select * from teacher where age between 25 and 30;+----+-------------+------+--------+
| id | name | age | salary |
+----+-------------+------+--------+
| 4 | meijianbiao | 30 | 9000 |
| 9 | tanghaolun | 30 | 50000 |
+----+-------------+------+--------+
2 rows in set (0.001 sec)
16.查找表teacher中以c开头的姓名的记录，再查找以ing结尾的姓名的记录，最后再查找以ing结尾或ao结尾的姓名的记录。
MariaDB [school]> select * from teacher where name like 'c%';+----+---------------+------+--------+
| id | name | age | salary |
+----+---------------+------+--------+
| 1 | chengsongling | 21 | 4000 |
| 2 | chengsongling | 21 | 4000 |
+----+---------------+------+--------+
2 rows in set (0.000sec)
MariaDB [school]> select * from teacher where name like '%ing';+----+---------------+------+--------+
| id | name | age | salary |
+----+---------------+------+--------+
| 1 | chengsongling | 21 | 4000 |
| 2 | chengsongling | 21 | 4000 |
+----+---------------+------+--------+
2 rows in set (0.000sec)
MariaDB [school]> select * from teacher where name like '%ing' or name like '%ao';+----+---------------+------+--------+
| id | name | age | salary |
+----+---------------+------+--------+
| 1 | chengsongling | 21 | 4000 |
| 2 | chengsongling | 21 | 4000 |
| 4 | meijianbiao | 30 | 9000 |
| 8 | yuqinhao | 50 | 100000 |
+----+---------------+------+--------+
4 rows in set (0.000 sec)
17.往表teacher里插入两条数据，再增加一行字段为department，默认为空，再把id为11的数据的department改为空格。
MariaDB [school]> insert teacher(name,age,salary) values('yanchuang',80,null),('chenben',69,0);
Query OK,2 rows affected (0.001sec)
Records:2 Duplicates: 0 Warnings: 0MariaDB [school]> select * fromteacher;+----+---------------+------+--------+
| id | name | age | salary |
+----+---------------+------+--------+
| 1 | chengsongling | 21 | 4000 |
| 2 | chengsongling | 21 | 4000 |
| 3 | taochi | 21 | 4000 |
| 4 | meijianbiao | 30 | 9000 |
| 5 | mufeng | 23 | 5000 |
| 6 | fangxinxin | 24 | 10000 |
| 7 | leichen | 21 | 10000 |
| 8 | yuqinhao | 50 | 100000 |
| 9 | tanghaolun | 30 | 50000 |
| 10 | yanchuang | 80 | NULL |
| 11 | chenben | 69 | 0 |
+----+---------------+------+--------+
11 rows in set (0.000sec)
MariaDB [school]> alter table teacher add department varchar(50) null;
Query OK,0 rows affected (0.001sec)
Records:0 Duplicates: 0 Warnings: 0MariaDB [school]> select * fromteacher;+----+---------------+------+--------+------------+
| id | name | age | salary | department |
+----+---------------+------+--------+------------+
| 1 | chengsongling | 21 | 4000 | NULL |
| 2 | chengsongling | 21 | 4000 | NULL |
| 3 | taochi | 21 | 4000 | NULL |
| 4 | meijianbiao | 30 | 9000 | NULL |
| 5 | mufeng | 23 | 5000 | NULL |
| 6 | fangxinxin | 24 | 10000 | NULL |
| 7 | leichen | 21 | 10000 | NULL |
| 8 | yuqinhao | 50 | 100000 | NULL |
| 9 | tanghaolun | 30 | 50000 | NULL |
| 10 | yanchuang | 80 | NULL | NULL |
| 11 | chenben | 69 | 0 | NULL |
+----+---------------+------+--------+------------+
11 rows in set (0.000sec)
MariaDB [school]> update teacher set department = ' ' where id = 11;
Query OK,1 row affected (0.001sec)
Rows matched:1 Changed: 1 Warnings: 0MariaDB [school]> select * fromteacher;+----+---------------+------+--------+------------+
| id | name | age | salary | department |
+----+---------------+------+--------+------------+
| 1 | chengsongling | 21 | 4000 | NULL |
| 2 | chengsongling | 21 | 4000 | NULL |
| 3 | taochi | 21 | 4000 | NULL |
| 4 | meijianbiao | 30 | 9000 | NULL |
| 5 | mufeng | 23 | 5000 | NULL |
| 6 | fangxinxin | 24 | 10000 | NULL |
| 7 | leichen | 21 | 10000 | NULL |
| 8 | yuqinhao | 50 | 100000 | NULL |
| 9 | tanghaolun | 30 | 50000 | NULL |
| 10 | yanchuang | 80 | NULL | NULL |
| 11 | chenben | 69 | 0 | |
+----+---------------+------+--------+------------+
11 rows in set (0.000 sec)
18.查找表teacher中dapartment数据不为空的数据。(数据中null等于空，空白不等于空)
MariaDB [school]> select * from teacher where department is not null;+----+---------+------+--------+------------+
| id | name | age | salary | department |
+----+---------+------+--------+------------+
| 11 | chenben | 69 | 0 | |
+----+---------+------+--------+------------+
1 row in set (0.000 sec)
19.先在表teacher里按age升序排列，再按salary降序排列。
MariaDB [school]> select * fromteacher order by age;+----+---------------+------+--------+------------+
| id | name | age | salary | department |
+----+---------------+------+--------+------------+
| 1 | chengsongling | 21 | 4000 | NULL |
| 2 | chengsongling | 21 | 4000 | NULL |
| 3 | taochi | 21 | 4000 | NULL |
| 7 | leichen | 21 | 10000 | NULL |
| 5 | mufeng | 23 | 5000 | NULL |
| 6 | fangxinxin | 24 | 10000 | NULL |
| 4 | meijianbiao | 30 | 9000 | NULL |
| 9 | tanghaolun | 30 | 50000 | NULL |
| 8 | yuqinhao | 50 | 100000 | NULL |
| 11 | chenben | 69 | 0 | |
| 10 | yanchuang | 80 | NULL | NULL |
+----+---------------+------+--------+------------+
11 rows in set (0.000sec)
MariaDB [school]> select * fromteacher order by salary desc;+----+---------------+------+--------+------------+
| id | name | age | salary | department |
+----+---------------+------+--------+------------+
| 8 | yuqinhao | 50 | 100000 | NULL |
| 9 | tanghaolun | 30 | 50000 | NULL |
| 6 | fangxinxin | 24 | 10000 | NULL |
| 7 | leichen | 21 | 10000 | NULL |
| 4 | meijianbiao | 30 | 9000 | NULL |
| 5 | mufeng | 23 | 5000 | NULL |
| 1 | chengsongling | 21 | 4000 | NULL |
| 3 | taochi | 21 | 4000 | NULL |
| 2 | chengsongling | 21 | 4000 | NULL |
| 11 | chenben | 69 | 0 | |
| 10 | yanchuang | 80 | NULL | NULL |
+----+---------------+------+--------+------------+
11 rows in set (0.000 sec)
20.先删除表teacher中工资为空的数据，再删除department不为空的数据。最后删除整个表teacher的数据。(使用delete命令删除，表依然会存在，且会保留表结构)
MariaDB [school]> delete from teacher where salary is null;
Query OK,1 row affected (0.050sec)
MariaDB [school]> select * fromteacher;+----+---------------+------+--------+------------+
| id | name | age | salary | department |
+----+---------------+------+--------+------------+
| 1 | chengsongling | 21 | 4000 | NULL |
| 2 | chengsongling | 21 | 4000 | NULL |
| 3 | taochi | 21 | 4000 | NULL |
| 4 | meijianbiao | 30 | 9000 | NULL |
| 5 | mufeng | 23 | 5000 | NULL |
| 6 | fangxinxin | 24 | 10000 | NULL |
| 7 | leichen | 21 | 10000 | NULL |
| 8 | yuqinhao | 50 | 100000 | NULL |
| 9 | tanghaolun | 30 | 50000 | NULL |
| 11 | chenben | 69 | 0 | |
+----+---------------+------+--------+------------+
10 rows in set (0.035sec)
MariaDB [school]> delete from teacher where department is not null;
Query OK,1 row affected (0.001sec)
MariaDB [school]> select *fromteacher;+----+---------------+------+--------+------------+
| id | name | age | salary | department |
+----+---------------+------+--------+------------+
| 1 | chengsongling | 21 | 4000 | NULL |
| 2 | chengsongling | 21 | 4000 | NULL |
| 3 | taochi | 21 | 4000 | NULL |
| 4 | meijianbiao | 30 | 9000 | NULL |
| 5 | mufeng | 23 | 5000 | NULL |
| 6 | fangxinxin | 24 | 10000 | NULL |
| 7 | leichen | 21 | 10000 | NULL |
| 8 | yuqinhao | 50 | 100000 | NULL |
| 9 | tanghaolun | 30 | 50000 | NULL |
+----+---------------+------+--------+------------+
9 rows in set (0.000sec)
MariaDB [school]> delete fromteacher;
Query OK,9 rows affected (0.001sec)
MariaDB [school]> select * fromteacher;
Emptyset (0.000sec)
MariaDB [school]>show tables;+------------------+
| Tables_in_school |
+------------------+
| student |
| teacher |
+------------------+
2 rows in set (0.000 sec)
21.再往teacher表里插入数据，会发现id还在顺延，使用truncate可以彻底删除。之后插入数据会发现id重新开始计数。(使用truncate删除的话数据无法恢复)
MariaDB [school]> insert teacher(name,age,salary) values('tom',20,8000),('jerry',23,6000),('zhangsan',22,9000);
Query OK,3 rows affected (0.001sec)
Records:3 Duplicates: 0 Warnings: 0MariaDB [school]> select * fromteacher;+----+----------+------+--------+------------+
| id | name | age | salary | department |
+----+----------+------+--------+------------+
| 12 | tom | 20 | 8000 | NULL |
| 13 | jerry | 23 | 6000 | NULL |
| 14 | zhangsan | 22 | 9000 | NULL |
+----+----------+------+--------+------------+
3 rows in set (0.000sec)
MariaDB [school]>truncate teacher;
Query OK,0 rows affected (0.008sec)
MariaDB [school]> select * fromteacher;
Emptyset (0.000sec)
MariaDB [school]> insert teacher(name,age,salary) values('tom',20,8000),('jerry',23,6000),('zhangsan',22,9000);
Query OK,3 rows affected (0.001sec)
Records:3 Duplicates: 0 Warnings: 0MariaDB [school]> select * fromteacher;+----+----------+------+--------+------------+
| id | name | age | salary | department |
+----+----------+------+--------+------------+
| 1 | tom | 20 | 8000 | NULL |
| 2 | jerry | 23 | 6000 | NULL |
| 3 | zhangsan | 22 | 9000 | NULL |
+----+----------+------+--------+------------+
3 rows in set (0.001 sec)
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