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给linux用户的11个高级MySQL数据库面试问题和答案
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================================================================================
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我们已经发表了两篇MySQL的文章,非常感谢Tecmint社区的大力支持.这是MySQL面试系列的第三篇文章,并且在面试专栏中排第16.
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- [15个基本的MySQL面试问题][1]
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- [给中级人员的10个MySQL面试问题][1]
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感谢你们这一路上对我们的支持.这篇文章主要针对MySQL的实用性,讲面试方面的问题.
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### 1. 如何使用SELECT语句找到你正在运行的服务器的版本并打印出当前数据库的名称? ###
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**Ans**:下面的语句的结果会显示服务器的版本和当前的数据库名称
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mysql> SELECT VERSION(), DATABASE();
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+-------------------------+------------+
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| VERSION() | DATABASE() |
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+-------------------------+------------+
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| 5.5.34-0ubuntu0.13.10.1 | NULL |
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+-------------------------+------------+
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1 row in set (0.06 sec)
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在Database一栏中显示**NULL**是因为我们当前没有选择任何数据库.因此,使用下面的语句先选择一个数据库,就能看到相应的结果.
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mysql> use Tecmint;
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Reading table information for completion of table and column names
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You can turn off this feature to get a quicker startup with -A
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Database changed
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----------
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mysql> select VERSION(), DATABASE();
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+-------------------------+------------+
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| VERSION() | DATABASE() |
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+-------------------------+------------+
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| 5.5.34-0ubuntu0.13.10.1 | tecmint |
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+-------------------------+------------+
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1 row in set (0.00 sec)
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### 2. 使用非运算符(!)从表"Tecmint"中列出除了user等于"SAM"的所有记录
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**Ans**:使用下面的语句
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mysql> SELECT * FROM Tecmint WHERE user !=SAM;
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+---------------------+---------+---------+---------+---------+-------+
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| date | user | host | root | local | size |
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+---------------------+---------+---------+---------+---------+-------+
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| 2001-05-14 14:42:21 | Anthony | venus | barb | venus | 98151 |
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| 2001-05-15 08:50:57 | TIM | venus | phil | venus | 978 |
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+---------------------+---------+---------+---------+---------+-------+
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### 3. 是否能够使用非运算符(!)来实现'AND'运算
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**Ans**: 我们使用’=’号和OR运算符或者'!='和AND运算符，下面是'='和AND运算符的例子
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mysql> SELECT * FROM mail WHERE user = SAM AND root = phil
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'!='和OR运算符的例子
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mysql> SELECT * FROM mail WHERE user != SAM OR root != phil
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+---------------------+---------+---------+---------+---------+-------+
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| date | user | host | root | local | size |
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+---------------------+---------+---------+---------+---------+-------+
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| 2001-05-14 14:42:21 | Anthony | venus | barb | venus | 98151 |
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+---------------------+---------+---------+---------+---------+-------+
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- = : 等于
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- != : 不等于
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- ! : 非运算符
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AND和OR在MySQL中被看作加入运算符
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### 4. IFNULL()语句在MySQL中有什么作用? ###
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**Ans**: **IFNULL**语句的使用使得MySQL中的查询更加精确。IFNULL()语句先测试它的的一个参数，若不为空就返回该参数的值，否则返回第二个参数的值
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mysql> SELECT name, IFNULL(id,'Unknown') AS 'id' FROM taxpayer;
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+---------+---------+
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| name | id |
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+---------+---------+
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| bernina | 198-48 |
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| bertha | Unknown |
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| ben | Unknown |
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| bill | 475-83 |
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+---------+---------+
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### 5. You want to see only certain rows from a result set from the beginning or end of a result set. How will you do it? ###
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### 5. 如果你只想知道从一个结果集的开头或者结尾开始的特定条数的行记录改如何实现？
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**Ans**: 我们可以用**LIMIT**和**ORDER BY**从句。
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#### Show 1 Record ####
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#### 显示一行记录 ####
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mysql> SELECT * FROM name LIMIT 1;
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+----+------+------------+-------+----------------------+------+
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| id | name | birth | color | foods | cats |
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+----+------+------------+-------+----------------------+------+
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| 1 | Fred | 1970-04-13 | black | lutefisk,fadge,pizza | 0 |
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+----+------+------------+-------+----------------------+------+
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#### 显示5行记录 ####
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mysql> SELECT * FROM profile LIMIT 5;
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+----+------+------------+-------+-----------------------+------+
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| id | name | birth | color | foods | cats |
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+----+------+------------+-------+-----------------------+------+
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| 1 | Fred | 1970-04-13 | black | lutefisk,fadge,pizza | 0 |
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| 2 | Mort | 1969-09-30 | white | burrito,curry,eggroll | 3 |
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| 3 | Brit | 1957-12-01 | red | burrito,curry,pizza | 1 |
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| 4 | Carl | 1973-11-02 | red | eggroll,pizza | 4 |
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| 5 | Sean | 1963-07-04 | blue | burrito,curry | 5 |
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+----+------+------------+-------+-----------------------+------+
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#### 显示按照ORDER BY排序后的第一条记录 ####
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mysql> SELECT * FROM profile ORDER BY birth LIMIT 1;
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+----+------+------------+-------+----------------+------+
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| id | name | birth | color | foods | cats |
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+----+------+------------+-------+----------------+------+
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| 9 | Dick | 1952-08-20 | green | lutefisk,fadge | 0 |
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+----+------+------------+-------+----------------+------+
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### 6. Oracle 和 MySQL.改如何选择? ###
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**Ans**: 它们都有各自的优点和缺点。
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#### 选择MySQL而不选orcale的原因 ####
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- 开源
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- 轻便快捷
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- 有命令行和图形界面
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- 能通过查询器进行数据库的管理
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### 7. MySQL中如何得到当前日期? ###
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**Ans**: 使用CURRENT_DATE()函数
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mysql> SELECT CURRENT_DATE();
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+----------------+
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| CURRENT_DATE() |
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+----------------+
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| 2014-06-17 |
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+----------------+
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### 8. How will you export tables as an XML file in MySQL? ###
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### 8. MySQL中如何将表导出为XML文件? ###
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**Ans**: 使用'-e'(export)参数来把MySQL表或整个数据库导出到XML文件。当处理大型表的时候或许我们需要手动导出，但是只是导出小文件的话可以直接使用想phpMyAdmin这样的工具。
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mysql -u USER_NAME –xml -e 'SELECT * FROM table_name' > table_name.xml
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Where USER_NAME is username of Database, table_name is the table we are exporting to XML and table_name.xml is the xml file where data is stored.
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### 9. What is MySQL_pconnect? And how it differs from MySQL_connect? ###
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**Ans**: MySQL_pconnect() opens a connection that is persistent to the MySQL Database which simply means that the database is not opened every-time the page loads and hence we can not use MySQL_close() to close a persistent connection.
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A brief difference between MySQL_pconnect and MySQL_connect are.
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Unlike MySQL_pconnect, MySQL_connect – Opens the Database every-time the page is loaded which can be closed any-time using statement MySQL_close().
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### 10. You need to show all the indexes defined in a table say ‘user’ of Database say ‘mysql’. How will you achieve this? ###
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**Ans**: The following command will show all the indexes of a table ‘user’.
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mysql> show index from user;
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+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
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| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
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+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
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| user | 0 | PRIMARY | 1 | Host | A | NULL | NULL | NULL | | BTREE | | |
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| user | 0 | PRIMARY | 2 | User | A | 4 | NULL | NULL | | BTREE | | |
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+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
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2 rows in set (0.00 sec)
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### 11. What are CSV tables? ###
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**Ans**: CSV stands for Comma-Separated Values aka Character-Separated Values. CSV table stores data in plain text and tabular format. It typically contains one record per line.
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Each record is separated by specific delimiters (Comma, Semi-colon, …) where each record has same sequence of field. CSV tables are most widely used to store phone contacts to Import and Export and can be used to store any sort of plain text data.
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That’s all for now. I’ll be here again with another Interesting article, you people will love to read. Till then stay tuned and connected to Tecmint and Don’t forget to provide us with your valuable feedback in the comment section below.
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--------------------------------------------------------------------------------
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via: http://www.tecmint.com/mysql-advance-interview-questions/
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译者：[译者ID](https://github.com/译者ID) 校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
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[1]:http://www.tecmint.com/basic-mysql-interview-questions-for-database-administrators/
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[2]:http://www.tecmint.com/10-mysql-database-interview-questions-for-beginners-and-intermediates/
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