15个 MySQL 基础面试题，DBA 们准备好了吗？
此前我们已经有发表过Linux 面试基础问答之一、二和三共3篇文章，获得读者的好评，同时我们得到反馈，有些读者希望这种交互式学习方法能够做得更加灵活。心动不如行动，我们这就为您奉上 15个 MySQL 面试题
问题1：你如何确定 MySQL 是否处于运行状态？
答案： Debian 上运行命令 service mysql status，在RedHat 上运行命令 service mysqld status。然后看看输出即可。
root@localhost:/home/avi# service mysql status
/usr/bin/mysqladmin Ver 8.42 Distrib 5.1.72, for debian-linux-gnu on i486
Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Server version 5.1.72-2
Protocol version 10
Connection Localhost via UNIX socket
UNIX socket /var/run/mysqld/mysqld.sock
Uptime: 1 hour 22 min 49 sec
Threads: 1 Questions: 112138 Slow queries: 1 Opens: 1485 Flush tables: 1 Open tables: 64 Queries per second avg: 22.567.问题2：如何开启或停止 MySQL 服务？
答案：运行命令 service mysqld start 开启服务；运行命令 service mysqld stop 停止服务。
root@localhost:/home/avi# service mysql stop
Stopping MySQL database server: mysqld.
root@localhost:/home/avi# service mysql start
Starting MySQL database server: mysqld.
Checking for corrupt, not cleanly closed and upgrade needing tables..
问题3：如何通过 Shell 登入 MySQL？
答案：运行命令 mysql -u root -p
root@localhost:/home/avi# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 207
Server version: 5.1.72-2 (Debian)
Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
问题4：如何列出所有数据库？
答案：运行命令 show databases;
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| a1 |
| cloud |
| mysql |
| phpmyadmin |
| playsms |
| sisso |
| test |
| ukolovnik |
| wordpress |
+--------------------+
10 rows in set (0.14 sec)
问题5： 如何切换到某个数据库并在上面工作？
答案：运行命令 use database_name; 进入名为 database_name 的数据库。
mysql> use cloud;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql>
问题6：如何列出某个数据库内所有表？
答案：在当前数据库运行命令 show tables;
mysql> show tables;
+----------------------------+
| Tables_in_cloud |
+----------------------------+
| oc_appconfig |
| oc_calendar_calendars |
| oc_calendar_objects |
| oc_calendar_repeat |
| oc_calendar_share_calendar |
| oc_calendar_share_event |
| oc_contacts_addressbooks |
| oc_contacts_cards |
| oc_fscache |
| oc_gallery_sharing |
+----------------------------+
10 rows in set (0.00 sec)
问题7：如何获取表内所有 Field 对象的名称和类型？
答案：运行命令 describe table_name;
mysql> describe oc_users;
+----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| uid | varchar(64) | NO | PRI | | |
| password | varchar(255) | NO | | | |
+----------+--------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
问题8：如何删除表？
答案：运行命令 drop table table_name;
mysql> drop table lookup;
Query OK, 0 rows affected (0.00 sec)
问题9：如何删除数据库？
答案：运行命令 drop database database-name;
mysql> drop database a1;
Query OK, 11 rows affected (0.07 sec)
问题10：如何查看表内所有数据？
答案：运行命令 select * from table_name;
mysql> select * from engines;
+------------+---------+----------------------------------------------------------------+--------------+------+------------+
| ENGINE | SUPPORT | COMMENT | TRANSACTIONS | XA | SAVEPOINTS |
+------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB | YES | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| CSV | YES | CSV storage engine | NO | NO | NO |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
| MyISAM | DEFAULT | Default engine as of MySQL 3.23 with great performance | NO | NO | NO |
+------------+---------+----------------------------------------------------------------+--------------+------+------------+
8 rows in set (0.00 sec)
问题11：如何从表（比如 oc_users ）中获取一个 field 对象（比如 uid）的所有数据？
答案：运行命令 select uid from oc_users;
mysql> select uid from oc_users;
+-----+
| uid |
+-----+
| avi |
+-----+
1 row in set (0.03 sec)
问题12：假设你有一个名为 ‘xyz’ 的表，它存在多个字段，如 ‘createtime’ 和 ‘engine’。名为 engine 的字段由 ‘Memoty’ 和 ‘MyIsam’ 两种数值组成。如何只列出 ‘createtime’ 和 ‘engine’ 这两列并且 engine 的值为 ‘MyIsam’？
答案：运行命令 select create_time, engine from xyz where engine = ”MyIsam”;
mysql> select create_time, engine from xyz where engine="MyIsam";
+---------------------+--------+
| create_time | engine |
+---------------------+--------+
| 2013-12-15 13:43:27 | MyISAM |
| 2013-12-15 13:43:27 | MyISAM |
| 2013-12-15 13:43:27 | MyISAM |
| 2013-12-15 13:43:27 | MyISAM |
| 2013-12-15 13:43:27 | MyISAM |
| 2013-12-15 13:43:27 | MyISAM |
| 2013-12-15 13:43:27 | MyISAM |
| 2013-12-15 13:43:27 | MyISAM |
| 2013-10-23 14:56:38 | MyISAM |
| 2013-10-23 14:56:38 | MyISAM |
| 2013-10-23 14:56:38 | MyISAM |
| 2013-10-23 14:56:38 | MyISAM |
| 2013-10-23 14:56:38 | MyISAM |
| 2013-10-23 14:56:38 | MyISAM |
| 2013-10-23 14:56:38 | MyISAM |
+---------------------+--------+
132 rows in set (0.29 sec)
问题13：如何列出表 ‘xrt’ 内 name 域值为 ‘tecmint’，web_address 域值为 ‘tecmint.com’ 的所有数据？
答案：运行命令 select * from xrt where name = “tecmint” and web_address = “tecmint.com”;
mysql> select * from xrt where name = "tecmint" and web_address = “tecmint.com”;
+---------------+---------------------+---------------+
| Id | name | web_address |
+---------------+---------------------+----------------+
| 13 | tecmint | tecmint.com |
+---------------+---------------------+----------------+
| 41 | tecmint | tecmint.com |
+---------------+---------------------+----------------+
问题14：如何列出表 ‘xrt’ 内 name 域值不为 ‘tecmint’，web_address 域值为 ‘tecmint.com’ 的所有数据？
答案：运行命令 select * from xrt where name != "tecmint" and web_address = "tecmint.com";
mysql> select * from xrt where name != ”tecmint” and web_address = ”tecmint.com”;
+---------------+---------------------+---------------+
| Id | name | web_address |
+---------------+---------------------+----------------+
| 1173 | tecmint | tecmint.com |
+---------------+---------------------+----------------+
问题15：如何知道表内行数？
答案：运行命令 select count(*) from table_name;
mysql> select count(*) from Tables;
+----------+
| count(*) |
+----------+
| 282 |
+----------+
1 row in set (0.01 sec)
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