MySQL必知必会面试题 基础
1、登录数据库
(1)、单实例
mysql -uroot -poldboy
(2)、多实例
mysql -uroot -poldboy -S /data/3306/mysql.sock
2、查看数据库版本及当前登录用户是什么
mysql> select version(); 查看版本
mysql> select user(); 查看用户
3、创建GBK字符集的数据库oldboy，并查看已建库的完整语句
mysql> create database oldboy character set gbk collate gbk_chinese_ci;
mysql> show create database oldboy\G
4、创建用户oldboy，使之可以管理数据库oldboy
第一种方法：
mysql> grant all on oldboy.* to oldboy@’localhost’ identified by ‘123456’;
mysql> select user,host from mysql.user;
第二种方法：
mysql> grant all on oldboy.* to oldboy@’192.168.1.%/255.255.255.0’ identified by ‘123456’;
mysql> select user,host from mysql.user;
第三种方法：
mysql> create user ‘abc’@’localhost’ identified by ‘123456’;
mysql> grant all on oldboy.* to ‘abc’@’localhost’;
5、查看创建的用户oldboy拥有哪些权限
mysql> show grants for abc@localhost;
mysql> show grants for oldboy@localhost;
mysql> show grants for oldboy@localhost\G
6、查看当前数据库有哪些用户
mysql> select user,host from mysql.user;
7、进入oldboy数据库
mysql> use oldboy
8、创建一innodb引擎字符集为GBK表test，字段为id和namevarchar(16)，查看建表结构及SQL语句
mysql> create table test(
-> id int(4),
-> name varchar(16)
-> )ENGINE=innodb default charset=gbk;
Query OK, 0 rows affected (0.02 sec)
第一种方法：
mysql> desc test;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(4) | YES | | NULL | |
| name | varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
第二种方法：
mysql> show columns from test;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(4) | YES | | NULL | |
| name | varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
查看表权限
mysql> show create table test;
9、插入一条数据 1，oldboy
mysql> insert into test values(1,'oldboy');
mysql> select * from test;
+------+--------+
| id | name |
+------+--------+
| 1 | oldboy |
+------+--------+
1 row in set (0.00 sec)
10、批量插入数据 2,老男孩，3,etiantian。ç要求中文不能乱码
mysql> insert into test values(2,'老男孩'),(3,'etiantian');
Query OK, 2 rows affected (0.07 sec)
Records: 2 Duplicates: 0 Warnings: 0
查看创建情况
mysql> select * from test;
+------+-----------+
| id | name |
+------+-----------+
| 1 | oldboy |
| 2 | 老男孩 |
| 3 | etiantian |
+------+-----------+
3 rows in set (0.00 sec)
11、查询插入的所有记录，查询名字为oldboy的记录。查询id大于1的记录。
（１）第一种方法
mysql> select * from test;
+------+-----------+
| id | name |
+------+-----------+
| 1 | oldboy |
| 2 | 老男孩 |
| 3 | etiantian |
+------+-----------+
3 rows in set (0.00 sec)
（２）第二种方法
mysql> select * from test where name='oldboy';
+------+--------+
| id | name |
+------+--------+
| 1 | oldboy |
+------+--------+
1 row in set (0.00 sec)
（３）第三种方法
mysql> select * from test where id>1;
+------+-----------+
| id | name |
+------+-----------+
| 2 | 老男孩 |
| 3 | etiantian |
+------+-----------+
2 rows in set (0.00 sec)
12、把数据id等于1的名字oldboy更改为oldgirl
mysql> update test set name='oldgirl' where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
查看修改情况
mysql> select * from test;
+------+-----------+
| id | name |
+------+-----------+
| 1 | oldgirl |
| 2 | 老男孩 |
| 3 | etiantian |
+------+-----------+
3 rows in set (0.00 sec)
13、在字段name前插入age字段，类型tinyint(2)
mysql> alter table test add age tinyint(2) after id;
Query OK, 3 rows affected (0.04 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> desc test;
+-------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+| id | int(4) | YES | | NULL | |
| age | tinyint(2) | YES | | NULL | |
| name | varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
14、备份oldboy库及MySQL库
mysqldump -uroot -poldboy -S /data/3306/mysql.sock --events -B oldboy mysql >/opt/mysql_back.sql
cat /opt/mysql_back.sql
15、删除表中的所有数据，并查看
第一种mysql> delete from test;
第二种mysql> truncate table test;
mysql> select * from test;
Empty set (0.00 sec)
16、删除表test和oldboy数据库并查看
mysql> drop table test; 删除表
mysql> drop database test; 删除库
17、Linux命令行恢复以上删除的数据
mysql -uroot -poldboy -S /data/3306/mysql.sock </opt/mysql_back.sql
18、把GBK字符集修改为UTF8（可选，注意，此题有陷阱）
mysql> show variables like 'character_set_%';
+--------------------------+-------------------------------------------+
| Variable_name | Value |
+--------------------------+-------------------------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /application/mysql-5.5.49/share/charsets/ |
由配置文件设置
+--------------------------+-------------------------------------------+8 rows in set (0.00 sec)
思想：
1、停止MySQL，单例可以使用/etc/init.d/mysqld（编译的话需要设置，yum安装就会出现）
多实例：/data/3306/mysql shutdown或者是/data/3306/mysql stop 这个需要我们自己写脚本。官方有参考
2、cp /etc/my.cnf /etc/my.cnf.bak,修改前做备份，这是个好习惯。
修改my.cnf
vi /etc/my.cnf
在[client]下添加，client为控制客户端的，没试过，没有的可以不需要加。
default-character-set=utf8
在[mysqld]下添加，mysqld为控制服务器端的，改过了，OK。
default-character-set=utf8
3.重启：yum安装可以使用/etc/init.d/mysqld start 多实例要使用/data/3306/mysql restart（多实例详细介绍见下一篇文章）
4.show variables like ‘%char%’;查看
19、MySQL密码丢了，如何找回实战？
单实例
/etc/init.d/mysqld stop
mysqld_safe --skip-grant-tables --user=mysql &
mysql
修改完密码重启
/etc/init.d/mysqld restart
多实例
/data/3306/mysql stop 无法停止
killall mysqld
mysqld_safe --defaults-file=/data/3306/my.cnf --skip-grant-tables --user=mysql &
update mysql.user set password=password('oldboy456') where user='root' and host='localhost';
flush privileges;
mysql 登录
mysqladmin -uroot -poldboy shutdown
/etc/init.d/mysqld start
原创申明：老男孩教育公众号文章均出自老男孩教育老师及学员原创，转载请联系miaokm@oldboyedu.com。
