mysql存储引擎类型都有哪些
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1、MyISAM
使用这个存储引擎，每个MyISAM在磁盘上存储成三个文件。
（1）frm文件：存储表的定义数据
（2）MYD文件：存放表具体记录的数据
（3）MYI文件：存储索引
frm和MYI可以存放在不同的目录下。MYI文件用来存储索引，但仅保存记录所在页的指针，索引的结构是B+树结构。下面这张图就是MYI文件保存的机制：
从这张图可以发现，这个存储引擎通过MYI的B+树结构来查找记录页，再根据记录页查找记录。并且支持全文索引、B树索引和数据压缩。
支持数据的类型也有三种：
（1）静态固定长度表
这种方式的优点在于存储速度非常快，容易发生缓存，而且表发生损坏后也容易修复。缺点是占空间。这也是默认的存储格式。
（2）动态可变长表
优点是节省空间，但是一旦出错恢复起来比较麻烦。
（3）压缩表
上面说到支持数据压缩，说明肯定也支持这个格式。在数据文件发生错误时候，可以使用check table工具来检查，而且还可以使用repair table工具来恢复。
有一个重要的特点那就是不支持事务，但是这也意味着他的存储速度更快，如果你的读写操作允许有错误数据的话，只是追求速度，可以选择这个存储引擎。
2、InnoDB
InnoDB是默认的数据库存储引擎，他的主要特点有：
（1）可以通过自动增长列，方法是auto_increment。
（2）支持事务。默认的事务隔离级别为可重复度，通过MVCC（并发版本控制）来实现的。
（3）使用的锁粒度为行级锁，可以支持更高的并发；
（4）支持外键约束；外键约束其实降低了表的查询速度，但是增加了表之间的耦合度。
（5）配合一些热备工具可以支持在线热备份；
（6）在InnoDB中存在着缓冲管理，通过缓冲池，将索引和数据全部缓存起来，加快查询的速度；
（7）对于InnoDB类型的表，其数据的物理组织形式是聚簇表。所有的数据按照主键来组织。数据和索引放在一块，都位于B+数的叶子节点上；
当然InnoDB的存储表和索引也有下面两种形式：
（1）使用共享表空间存储：所有的表和索引存放在同一个表空间中。
（2）使用多表空间存储：表结构放在frm文件，数据和索引放在IBD文件中。分区表的话，每个分区对应单独的IBD文件，分区表的定义可以查看我的其他文章。使用分区表的好处在于提升查询效率。
对于InnoDB来说，最大的特点在于支持事务。但是这是以损失效率来换取的。
3、Memory
将数据存在内存，为了提高数据的访问速度，每一个表实际上和一个磁盘文件关联。文件是frm。
（1）支持的数据类型有限制，比如：不支持TEXT和BLOB类型，对于字符串类型的数据，只支持固定长度的行，VARCHAR会被自动存储为CHAR类型；
（2）支持的锁粒度为表级锁。所以，在访问量比较大时，表级锁会成为MEMORY存储引擎的瓶颈；
（3）由于数据是存放在内存中，一旦服务器出现故障，数据都会丢失；
（4）查询的时候，如果有用到临时表，而且临时表中有BLOB，TEXT类型的字段，那么这个临时表就会转化为MyISAM类型的表，性能会急剧降低；
（5）默认使用hash索引。
（6）如果一个内部表很大，会转化为磁盘表。
在这里只是给出3个常见的存储引擎。使用哪一种引擎需要灵活选择，一个数据库中多个表可以使用不同引擎以满足各种性能和实际需求，使用合适的存储引擎，将会提高整个数据库的性能
参考技术A 一般我们储存的引擎软件有很多，就比如说像我们自己的固态硬盘，储存机械，硬盘储存，还有自己的这个手机上的内存卡储存，一般都是通过这些一个小卡片来储存当前的这些数据的。MySQL存储引擎 SQL数据导入/导出 操作表记录 查询及匹配条件
MySQL存储引擎的配置
SQL数据导入/导出
操作表记录
查询及匹配条件1 MySQL存储引擎的配置
1.1 问题
本案例要求MySQL数据存储引擎的使用，完成以下任务操作：
可用的存储引擎类型
查看默认存储类型
更改表的存储引擎1.2 步骤
实现此案例需要按照如下步骤进行。
步骤一：查看存储引擎信息
登入MySQL服务器，查看当前支持哪些存储引擎。
使用mysql命令连接，以root用户登入：
[[email protected] ~]# mysql -u root –p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 9
Server version: 5.7.17 MySQL Community Server (GPL)
Copyright (c) 2000, 2016, 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> 执行SHOW ENGINESG指令可列表查看，MySQL 5.6可用的存储引擎有9种（除最后的FEDERATED以外，其他8种都支持），其中默认采用的存储引擎为InnoDB：
mysql> SHOW ENGINESG
*************************** 1. row ***************************
Engine: InnoDB
Support: DEFAULT //此存储引擎为默认
Comment: Supports transactions, row-level locking, and foreign keys
Transactions: YES
XA: YES
Savepoints: YES
*************************** 2. row ***************************
Engine: MRG_MYISAM
Support: YES
Comment: Collection of identical MyISAM tables
Transactions: NO
XA: NO
Savepoints: NO
*************************** 3. row ***************************
Engine: MEMORY
Support: YES
Comment: Hash based, stored in memory, useful for temporary tables
Transactions: NO
XA: NO
Savepoints: NO
*************************** 4. row ***************************
Engine: BLACKHOLE
Support: YES
Comment: /dev/null storage engine (anything you write to it disappears)
Transactions: NO
XA: NO
Savepoints: NO
*************************** 5. row ***************************
Engine: MyISAM
Support: YES
Comment: MyISAM storage engine
Transactions: NO
XA: NO
Savepoints: NO
*************************** 6. row ***************************
Engine: CSV
Support: YES
Comment: CSV storage engine
Transactions: NO
XA: NO
Savepoints: NO
*************************** 7. row ***************************
Engine: ARCHIVE
Support: YES
Comment: Archive storage engine
Transactions: NO
XA: NO
Savepoints: NO
*************************** 8. row ***************************
Engine: PERFORMANCE_SCHEMA
Support: YES
Comment: Performance Schema
Transactions: NO
XA: NO
Savepoints: NO
*************************** 9. row ***************************
Engine: FEDERATED
Support: NO //此引擎不被支持
Comment: Federated MySQL storage engine
Transactions: NULL
XA: NULL
Savepoints: NULL
9 rows in set (0.01 sec)或者直接查看系统变量default_storage_engine 的值，也可确认默认采用的存储引擎是InnoDB：
mysql> SHOW VARIABLES LIKE ‘default_storage_engine‘;
+------------------------+--------+
| Variable_name | Value |
+------------------------+--------+
| default_storage_engine | InnoDB |
+------------------------+--------+
1 row in set (0.00 sec)步骤二：修改默认存储引擎
在 mysql> 环境中，可以直接通过SET指令更改默认的存储引擎（只在本次连接会话过程中有效，退出重进即失效） 。比如临时修改为MyISAM，可执行下列操作：
mysql> SET default_storage_engine=MyISAM; //改用MyISAM引擎
Query OK, 0 rows affected (0.00 sec)
mysql> SHOW VARIABLES LIKE ‘default_storage_engine‘; //确认结果
+------------------------+--------+
| Variable_name | Value |
+------------------------+--------+
| default_storage_engine | MyISAM |
+------------------------+--------+
1 row in set (0.00 sec)若希望直接修改MySQL服务程序所采用的默认存储引擎，应将相关设置写入配置文件/etc/my.cnf，并重启服务后生效。比如：
[[email protected] ~]# vim /etc/my.cnf
[mysqld]
.. ..
default_storage_engine=MEMORY //改用MEMORY引擎
[[email protected] ~]# systemctl restart mysqld.service //重启服务重新登入 mysql> 确认修改结果：
[[email protected] ~]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 3
Server version: 5.7.17 MySQL Community Server (GPL)
Copyright (c) 2000, 2016, 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> SHOW VARIABLES LIKE ‘default_storage_engine‘;
+------------------------+--------+
| Variable_name | Value |
+------------------------+--------+
| default_storage_engine | MEMORY | //默认引擎已修改
+------------------------+--------+
1 row in set (0.00 sec)
mysql> exit
Bye为了避免后续实验障碍，测试完后记得恢复原状——移除默认引擎设置，或者将其修改为InnoDB即可：
[[email protected] ~]# vim /etc/my.cnf
[mysqld]
.. ..
default_storage_engine=InnoDB
[[email protected] ~]# systemctl restart mysqld.service确认恢复结果（选项 -e 可调用指定的SQL操作后返回Shell命令行）：
[[email protected] ~]# mysql -u root -p -e "SHOW VARIABLES LIKE ‘default_storage_engine‘;"
Enter password:
+------------------------+--------+
| Variable_name | Value |
+------------------------+--------+
| default_storage_engine | InnoDB |
+------------------------+--------+2 SQL数据导入/导出
2.1 问题
使用SQL语句完成下列导出、导入操作：
将/etc/passwd文件导入userdb库userlist表并给每条记录加编号
将userdb库userlist表中UID小于100的前10条记录导出，存为/dbak/ulist.txt文件2.2 步骤
实现此案例需要按照如下步骤进行。
步骤一：将/etc/passwd文件导入MySQL数据库
导入后的表结构取决于/etc/passwd配置文件。若一时记不住各字段的含义，也可以查看passwd配置文件的man手册页，找到格式描述相关的说明，比如：
[[email protected] ~]# man 5 passwd
.. ..
Each line of the file describes a single user, and contains seven colon-sep‐
arated fields:
name:password:UID:GID:GECOS:directory:shell //各字段的顺序、大致用途
The field are as follows: //以下详细解释各字段的作用
name This is the user‘s login name. It should not contain capital
letters.
password This is either the encrypted user password, an asterisk (*), or
the letter ‘x‘. (See pwconv(8) for an explanation of ‘x‘.)
UID The privileged root login account (superuser) has the user ID 0.
GID This is the numeric primary group ID for this user. (Additional
groups for the user are defined in the system group file; see
group(5)).
GECOS stands for "General Electric Comprehensive Operating Sys‐
tem", which was renamed to GCOS when GE‘s large systems division
was sold to Honeywell. Dennis Ritchie has reported: "Sometimes
we sent printer output or batch jobs to the GCOS machine. The
gcos field in the password file was a place to stash the infor‐
mation for the $IDENTcard. Not elegant."
directory This is the user‘s home directory: the initial directory where
the user is placed after logging in. The value in this field is
used to set the HOME environment variable.
shell This is the program to run at login (if empty, use /bin/sh). If
set to a nonexistent executable, the user will be unable to
login through login(1). The value in this field is used to set
the SHELL environment variable.
.. ..1）新建userdb库、userlist表
以数据库用户root登入MySQL服务：
[[email protected] ~]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 5
Server version: 5.7.17 MySQL Community Server (GPL)
Copyright (c) 2000, 2016, 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> 新建userdb库，切换到userdb库：
mysql> CREATE DATABASE userdb;
Query OK, 1 row affected (0.00 sec)
mysql> USE userdb;
Database changed新建userlist表，字段设置及相关操作参考如下：
mysql> CREATE TABLE userlist(
-> username varchar(24) NOT NULL,
-> password varchar(48) DEFAULT ‘x‘,
-> uid int(5) NOT NULL,
-> gid int(5) NOT NULL,
-> fullname varchar(48),
-> homedir varchar(64) NOT NULL,
-> shell varchar(24) NOT NULL
-> );
Query OK, 0 rows affected (0.70 sec)确认userlist表的结构：
mysql> DESC userlist;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| username | varchar(24) | NO | | NULL | |
| password | varchar(48) | YES | | x | |
| uid | int(5) | NO | | NULL | |
| gid | int(5) | NO | | NULL | |
| fullname | varchar(48) | YES | | NULL | |
| homedir | varchar(64) | NO | | NULL | |
| shell | varchar(24) | NO | | NULL | |
+----------+-------------+------+-----+---------+-------+
7 rows in set (0.01 sec)2）如果直接导入会报错。在MySQL 5.7.6版本之后，导入文件只能在secure_file_priv指定的文件夹下。执行show variables like ‘%secure%‘命令显示文件目录：
mysql> LOAD DATA INFILE ‘/etc/passwd‘ INTO TABLE userlist FIELDS TERMINATED BY ‘:‘;
ERROR 1290 (HY000): The MySQL server is running with the --secure-file-priv option so it cannot execute this statement
mysql> show variables like ‘%secure%‘;
+--------------------------+-----------------------+
| Variable_name | Value |
+--------------------------+-----------------------+
| require_secure_transport | OFF |
| secure_auth | ON |
| secure_file_priv | /var/lib/mysql-files/ |
+--------------------------+-----------------------+
3 rows in set (0.00 sec)3）执行导入操作
将/etc/passwd文件复制到/var/lib/mysql-files/目录下，
读取/var/lib/mysql-files/passwd文件内容，以“:”为分隔，导入到userlist表中：
[[email protected] ~]#cp /etc/passwd /var/lib/mysql-files/
mysql> LOAD DATA INFILE ‘/var/lib/mysql-files/passwd‘
-> INTO TABLE userlist
-> FIELDS TERMINATED BY ‘:‘;
Query OK, 39 rows affected (0.11 sec)
Records: 39 Deleted: 0 Skipped: 0 Warnings: 0上述操作中省略了行分隔 LINES TERMINATED BY ‘ ‘，因为这是默认的情况（每行一条原始记录），除非需要以其他字符分割行，才需要用到这个。比如，以下操作指定了行分隔为‘ ‘，将/var/lib/mysql-files/passwd文件的内容导入另一个表userlist2，最终userlist2表的内容与userlsit的内容是一样的：
代码
4）确认导入结果
分别统计userlist、userlist2表内的记录个数：
mysql> SELECT COUNT(*) FROM userlist;
+----------+
| COUNT(*) |
+----------+
| 39 | //userlist表有39条记录
+----------+
1 row in set (0.00 sec)
mysql> SELECT COUNT(*) FROM userlist2;
+----------+
| COUNT(*) |
+----------+
| 39 | //userlist表也有39条记录
+----------+
1 row in set (0.00 sec)查看userlist表的前10条记录，列出用户名、UID、GID、宿主目录、登录Shell：
mysql> SELECT username,uid,gid,homedir,shell
-> FROM userlist LIMIT 10;
+----------+-----+-----+-----------------+----------------+
| username | uid | gid | homedir | shell |
+----------+-----+-----+-----------------+----------------+
| root | 0 | 0 | /root | /bin/bash |
| bin | 1 | 1 | /bin | /sbin/nologin |
| daemon | 2 | 2 | /sbin | /sbin/nologin |
| adm | 3 | 4 | /var/adm | /sbin/nologin |
| lp | 4 | 7 | /var/spool/lpd | /sbin/nologin |
| sync | 5 | 0 | /sbin | /bin/sync |
| shutdown | 6 | 0 | /sbin | /sbin/shutdown |
| halt | 7 | 0 | /sbin | /sbin/halt |
| mail | 8 | 12 | /var/spool/mail | /sbin/nologin |
| operator | 11 | 0 | /root | /sbin/nologin |
+----------+-----+-----+-----------------+----------------+
10 rows in set (0.00 sec)查看userlist2表的前10条记录，同样列出用户名、UID、GID、宿主目录、登录Shell：
mysql> SELECT username,uid,gid,homedir,shell
-> FROM userlist2 LIMIT 10;
+----------+-----+-----+-----------------+----------------+
| username | uid | gid | homedir | shell |
+----------+-----+-----+-----------------+----------------+
| root | 0 | 0 | /root | /bin/bash |
| bin | 1 | 1 | /bin | /sbin/nologin |
| daemon | 2 | 2 | /sbin | /sbin/nologin |
| adm | 3 | 4 | /var/adm | /sbin/nologin |
| lp | 4 | 7 | /var/spool/lpd | /sbin/nologin |
| sync | 5 | 0 | /sbin | /bin/sync |
| shutdown | 6 | 0 | /sbin | /sbin/shutdown |
| halt | 7 | 0 | /sbin | /sbin/halt |
| mail | 8 | 12 | /var/spool/mail | /sbin/nologin |
| operator | 11 | 0 | /root | /sbin/nologin |
+----------+-----+-----+-----------------+----------------+
10 rows in set (0.00 sec)步骤二：为userlist表中的每条记录添加自动编号
这个只要修改userlist表结构，添加一个自增字段即可。
比如，添加一个名为sn的序号列，作为userlist表的第一个字段：
1）添加自增主键字段sn
mysql> ALTER TABLE userlist
-> ADD sn int(4) AUTO_INCREMENT PRIMARY KEY FIRST;
Query OK, 0 rows affected (0.62 sec)
Records: 0 Duplicates: 0 Warnings: 02）验证自动编号结果
查看userlist表的前10条记录，列出序号、用户名、UID、GID、宿主目录：
mysql> SELECT sn,username,uid,gid,homedir
-> FROM userlist LIMIT 10;
+----+----------+-----+-----+-----------------+
| sn | username | uid | gid | homedir |
+----+----------+-----+-----+-----------------+
| 1 | root | 0 | 0 | /root |
| 2 | bin | 1 | 1 | /bin |
| 3 | daemon | 2 | 2 | /sbin |
| 4 | adm | 3 | 4 | /var/adm |
| 5 | lp | 4 | 7 | /var/spool/lpd |
| 6 | sync | 5 | 0 | /sbin |
| 7 | shutdown | 6 | 0 | /sbin |
| 8 | halt | 7 | 0 | /sbin |
| 9 | mail | 8 | 12 | /var/spool/mail |
| 10 | operator | 11 | 0 | /root |
+----+----------+-----+-----+-----------------+
10 rows in set (0.00 sec)步骤三：从MySQL数据库中导出查询结果
以将userdb库userlist表中UID小于100的前10条记录导出为/var/lib/mysql-files/ulist.txt文件为例。
1）确认存放导出数据的文件夹
[[email protected] ~]# ls -ld /var/lib/mysql-files/
drwxr-x---. 2 mysql mysql 19 4月 7 11:15 /var/lib/mysql-files/2）导出userlsit表中UID小于100的前10条记录
如果以默认的‘ ‘ 为行分隔，导出操作同样可不指定LINES TERMINATED BY：
mysql> SELECT * FROM userdb.userlist WHERE uid<100
-> INTO OUTFILE ‘/var/lib/mysql-files/ulist.txt‘
-> FIELDS TERMINATED BY ‘:‘;
Query OK, 24 rows affected (0.00 sec)3）确认导出结果
返回到Shell命令行，查看/var/lib/mysql-files/ulist.txt文件的行数：
[[email protected] ~]# wc -l /var/lib/mysql-files/ulist.txt
24 /var/lib/mysql-files/ulist.txt查看/var/lib/mysql-files/ulist.txt文件的最后10行内容：
[[email protected] ~]# tail /var/lib/mysql-files/ulist.txt
19:avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin
24:rpc:x:32:32:Rpcbind Daemon:/var/lib/rpcbind:/sbin/nologin
25:rpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologin
28:radvd:x:75:75:radvd user:/:/sbin/nologin
29:ntp:x:38:38::/etc/ntp:/sbin/nologin
33:gdm:x:42:42::/var/lib/gdm:/sbin/nologin
35:postfix:x:89:89::/var/spool/postfix:/sbin/nologin
36:sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
37:tcpdump:x:72:72::/:/sbin/nologin
39:mysql:x:27:27:MySQL Server:/var/lib/mysql:/bin/false3 操作表记录
3.1 问题
练习表记录的操作
表记录的插入
表记录的更新
表记录的查询
表记录的删除3.2 步骤
实现此案例需要按照如下步骤进行。
步骤一：创建stu_info表，并确保stu_info表记录为空。
在userdb库中创建stu_info表：
[[email protected] ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 19
Server version: 5.7.17 MySQL Community Server (GPL)
Copyright (c) 2000, 2016, 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> use userdb;
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> CREATE TABLE stu_info(
-> name varchar(12) NOT NULL,
-> gender enum(‘boy‘,‘girl‘) DEFAULT ‘boy‘,
-> age int(3) NOT NULL
-> );
Query OK, 0 rows affected (0.23 sec)删除stu_info表的所有记录：
mysql> DELETE FROM stu_info;
Query OK, 0 rows affected (0.00 sec) //stu_info表刚建立 删除零条记录确认删除结果：
mysql> SELECT * FROM stu_info;
Empty set (0.00 sec)步骤二：练习表记录的操作
1）插入记录时，指定记录的每一个字段的值
这种情况下，不需要明确指出字段，但每条记录的值的顺序、类型都必须与表格结构向一致，否则可能无法正确插入记录。
比如，以下操作将向stu_info表插入3条表记录：
mysql> INSERT stu_info VALUES
-> (‘Jim‘,‘girl‘,24),
-> (‘Tom‘,‘boy‘,21),
-> (‘Lily‘,‘girl‘,20);
Query OK, 3 rows affected (0.15 sec)
Records: 3 Duplicates: 0 Warnings: 0完成插入后确认表记录：
mysql> SELECT * FROM stu_info;
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Jim | girl | 24 |
| Tom | boy | 21 |
| Lily | girl | 20 |
+------+--------+-----+
3 rows in set (0.00 sec)2）插入记录时，只指定记录的部分字段的值
这种情况下，必须指出各项值所对应的字段；而且，未赋值的字段应设置有默认值或者有自增填充属性或者允许为空，否则插入操作将会失败。
比如，向stu_info表插入Jerry的年龄信息，性别为默认的“boy”，自动编号，相关操作如下：
mysql> INSERT INTO stu_info(name,age)
-> VALUES(‘Jerry‘,27);
Query OK, 1 row affected (0.04 sec)类似的，再插入用户Mike的年龄信息：
mysql> INSERT INTO stu_info(name,age)
-> VALUES(‘Mike‘,21);
Query OK, 1 row affected (0.05 sec)确认目前stu_info表的所有记录：
mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 24 |
| Tom | boy | 21 |
| Lily | girl | 20 |
| Jerry | boy | 27 |
| Mike | boy | 21 |
+-------+--------+-----+
5 rows in set (0.00 sec)3）更新表记录时，若未限制条件，则适用于所有记录
将stu_info表中所有记录的age设置为10：
mysql> UPDATE stu_info SET age=10;
Query OK, 5 rows affected (0.04 sec)
Rows matched: 5 Changed: 5 Warnings: 0确认更新结果：
mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 10 |
| Tom | boy | 10 |
| Lily | girl | 10 |
| Jerry | boy | 10 |
| Mike | boy | 10 |
+-------+--------+-----+
5 rows in set (0.00 sec)4）更新表记录时，可以限制条件，只对符合条件的记录有效
将stu_info表中所有性别为“boy”的记录的age设置为20：
mysql> UPDATE stu_info SET age=20
-> WHERE gender=‘boy‘;
Query OK, 3 rows affected (0.04 sec)
Rows matched: 3 Changed: 3 Warnings: 0确认更新结果：
mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 10 |
| Tom | boy | 20 |
| Lily | girl | 10 |
| Jerry | boy | 20 |
| Mike | boy | 20 |
+-------+--------+-----+
5 rows in set (0.00 sec)5）删除表记录时，可以限制条件，只删除符合条件的记录
删除stu_info表中年龄小于18的记录：
mysql> DELETE FROM stu_info WHERE age < 18;
Query OK, 2 rows affected (0.03 sec)确认删除结果：
mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Tom | boy | 20 |
| Jerry | boy | 20 |
| Mike | boy | 20 |
+-------+--------+-----+
3 rows in set (0.00 sec)6）删除表记录时，如果未限制条件，则会删除所有的表记录
删除stu_info表的所有记录：
mysql> DELETE FROM stu_info;
Query OK, 3 rows affected (0.00 sec)确认删除结果：
mysql> SELECT * FROM stu_info;
Empty set (0.00 sec)4 查询及匹配条件
4.1 问题
练习常见的SQL查询及条件设置
创建stu_info表，并插入数据
练习常见SQL查询及条件设置4.2 步骤
实现此案例需要按照如下步骤进行。
步骤一：根据任务要求建立员工档案表stu_info（如上个实验已创建，可将上个实验stu_info表中记录清除后继续使用）
1）在userdb库中创建stu_info表
以root用户登入MySQL服务器：
[[email protected] ~]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 5
Server version: 5.6.15 MySQL Community Server (GPL)
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>打开test库：
mysql> USE userdb;
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创建stu_info表，包括name、gender、age三个字段：
mysql> CREATE TABLE stu_info(
-> name varchar(12) NOT NULL,
-> gender enum(‘boy‘,‘girl‘) DEFAULT ‘boy‘,
-> age int(3) NOT NULL
-> );
Query OK, 0 rows affected (0.03 sec)确认表结构：
mysql> DESC stu_info;
+--------+--------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------------+------+-----+---------+-------+
| name | varchar(12) | NO | | NULL | |
| gender | enum(‘boy‘,‘girl‘) | YES | | boy | |
| age | int(3) | NO | | NULL | |
+--------+--------------------+------+-----+---------+-------+
3 rows in set (0.01 sec)2）准备测试表格
向建立的stu_info表插入几条测试记录
mysql> INSERT INTO stu_info VALUES
-> (‘Jim‘,‘girl‘,24),
-> (‘Tom‘,‘boy‘,21),
-> (‘Lily‘,‘girl‘,20),
-> (‘Jerry‘,‘boy‘,27),
-> (‘Mike‘,‘boy‘,21)
-> ;
Query OK, 5 rows affected (0.06 sec)
Records: 5 Duplicates: 0 Warnings: 0确认stu_info表的所有记录内容：
mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 24 |
| Tom | boy | 21 |
| Lily | girl | 20 |
| Jerry | boy | 27 |
| Mike | boy | 21 |
+-------+--------+-----+
5 rows in set (0.00 sec)步骤二：练习常见SQL查询及条件设置
1）常用的表记录统计函数
查询stu_info表一共有多少条记录（本例中为5条）：
mysql> SELECT count(*) FROM stu_info;
+----------+
| count(*) |
+----------+
| 5 |
+----------+
1 row in set (0.00 sec)计算stu_info表中各学员的平均年龄、最大年龄、最小年龄：
mysql> SELECT avg(age),max(age),min(age) FROM stu_info;
+----------+----------+----------+
| avg(age) | max(age) | min(age) |
+----------+----------+----------+
| 22.6000 | 27 | 20 |
+----------+----------+----------+
1 row in set (0.00 sec)计算stu_info表中男学员的个数：
mysql> SELECT count(gender) FROM stu_info WHERE gender=‘boy‘;
+---------------+
| count(gender) |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)2）字段值的数值比较
列出stu_info表中年龄为21岁的学员记录：
mysql> SELECT * FROM stu_info WHERE age=21;
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Tom | boy | 21 |
| Mike | boy | 21 |
+------+--------+-----+
2 rows in set (0.00 sec)列出stu_info表中年龄超过21岁的学员记录：
mysql> SELECT * FROM stu_info WHERE age>21;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 24 |
| Jerry | boy | 27 |
+-------+--------+-----+
2 rows in set (0.00 sec)列出stu_info表中年龄大于或等于21岁的学员记录：
mysql> SELECT * FROM stu_info WHERE age>=21;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 24 |
| Tom | boy | 21 |
| Jerry | boy | 27 |
| Mike | boy | 21 |
+-------+--------+-----+
4 rows in set (0.00 sec)列出stu_info表中年龄在20岁和24岁之间的学员记录：
mysql> SELECT * FROM stu_info WHERE age BETWEEN 20 and 24;
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Jim | girl | 24 |
| Tom | boy | 21 |
| Lily | girl | 20 |
| Mike | boy | 21 |
+------+--------+-----+
4 rows in set (0.00 sec)3）多个条件的组合
列出stu_info表中年龄小于23岁的女学员记录：
mysql> SELECT * FROM stu_info WHERE age < 23 AND gender=‘girl‘;
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Lily | girl | 20 |
+------+--------+-----+
1 row in set (0.00 sec)列出stu_info表中年龄小于23岁的学员，或者女学员的记录：
mysql> SELECT * FROM stu_info WHERE age < 23 OR gender=‘girl‘;
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Jim | girl | 24 |
| Tom | boy | 21 |
| Lily | girl | 20 |
| Mike | boy | 21 |
+------+--------+-----+
4 rows in set (0.00 sec)如果某个记录的姓名属于指定范围内的一个，则将其列出：
mysql> SELECT * FROM stu_info WHERE name IN
-> (‘Jim‘,‘Tom‘,‘Mickey‘,‘Minnie‘);
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Jim | girl | 24 |
| Tom | boy | 21 |
+------+--------+-----+
2 rows in set (0.00 sec)4）使用SELECT做数学计算
计算1234与5678的和：
mysql> SELECT 1234+5678;
+-----------+
| 1234+5678 |
+-----------+
| 6912 |
+-----------+
1 row in set (0.00 sec)计算1234与5678的乘积：
mysql> SELECT 1234*5678;
+-----------+
| 1234*5678 |
+-----------+
| 7006652 |
+-----------+
1 row in set (0.00 sec)计算1.23456789除以3的结果：
mysql> SELECT 1.23456789/3;
+----------------+
| 1.23456789/3 |
+----------------+
| 0.411522630000 |
+----------------+
1 row in set (0.00 sec)输出stu_info表各学员的姓名、15年后的年龄：
mysql> SELECT name,age+15 FROM stu_info;
+-------+--------+
| name | age+15 |
+-------+--------+
| Jim | 39 |
| Tom | 36 |
| Lily | 35 |
| Jerry | 42 |
| Mike | 36 |
+-------+--------+
5 rows in set (0.00 sec)5）使用模糊查询，LIKE引领
以下划线 _ 匹配单个字符，% 可匹配任意多个字符。
列出stu_info表中姓名以“J”开头的学员记录：
mysql> SELECT * FROM stu_info WHERE name LIKE ‘J%‘;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 24 |
| Jerry | boy | 27 |
+-------+--------+-----+
2 rows in set (0.00 sec)列出stu_info表中姓名以“J”开头且只有3个字母的学员记录：
mysql> SELECT * FROM stu_info WHERE name LIKE ‘J__‘;
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Jim | girl | 24 |
+------+--------+-----+
1 row in set (0.00 sec)6）使用正则表达式，REGEXP引领
列出stu_info表中姓名以“J”开头且以“y”结尾的学员记录：
mysql> SELECT * FROM stu_info WHERE name REGEXP ‘^J.*y$‘;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jerry | boy | 27 |
+-------+--------+-----+
1 row in set (0.00 sec)效果等同于：
mysql> SELECT * FROM stu_info WHERE name Like ‘J%y‘;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jerry | boy | 27 |
+-------+--------+-----+
1 row in set (0.00 sec)列出stu_info表中姓名以“J”开头或者以“y”结尾的学员记录：
mysql> SELECT * FROM stu_info WHERE name REGEXP ‘^J|y$‘;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 24 |
| Lily | girl | 20 |
| Jerry | boy | 27 |
+-------+--------+-----+
3 rows in set (0.00 sec)效果等同于：
mysql> SELECT * FROM stu_info WHERE name Like ‘J%‘ OR name Like ‘%y‘;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jim | girl | 24 |
| Lily | girl | 20 |
| Jerry | boy | 27 |
+-------+--------+-----+
3 rows in set (0.00 sec)7）按指定的字段排序，ORDER BY
列出stu_info表的所有记录，按年龄排序：
mysql> SELECT * FROM stu_info GROUP BY age;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Lily | girl | 20 |
| Tom | boy | 21 |
| Jim | girl | 24 |
| Jerry | boy | 27 |
+-------+--------+-----+
4 rows in set (0.00 sec)因默认为升序（Ascend）排列，所以上述操作等效于：
mysql> SELECT * FROM stu_info GROUP BY age ASC;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Lily | girl | 20 |
| Tom | boy | 21 |
| Jim | girl | 24 |
| Jerry | boy | 27 |
+-------+--------+-----+
4 rows in set (0.00 sec)若要按降序（Descend）排列，则将ASC改为DESC即可：
mysql> SELECT * FROM stu_info GROUP BY age DESC;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jerry | boy | 27 |
| Jim | girl | 24 |
| Tom | boy | 21 |
| Lily | girl | 20 |
+-------+--------+-----+
4 rows in set (0.00 sec)8）限制查询结果的输出条数，LIMIT
查询stu_info表的所有记录，只列出前3条：
mysql> SELECT * FROM stu_info LIMIT 3;
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Jim | girl | 24 |
| Tom | boy | 21 |
| Lily | girl | 20 |
+------+--------+-----+
3 rows in set (0.00 sec)列出stu_info表中年龄最大的3条学员记录：
mysql> SELECT * FROM stu_info GROUP BY age DESC LIMIT 3;
+-------+--------+-----+
| name | gender | age |
+-------+--------+-----+
| Jerry | boy | 27 |
| Jim | girl | 24 |
| Tom | boy | 21 |
+-------+--------+-----+
3 rows in set (0.00 sec)9）分组查询结果，GROUP BY
针对stu_info表，按性别分组，分别统计出男、女学员的人数：
mysql> SELECT gender,count(gender) FROM stu_info GROUP BY gender;
+--------+---------------+
| gender | count(gender) |
+--------+---------------+
| boy | 3 |
| girl | 2 |
+--------+---------------+
2 rows in set (0.00 sec)列出查询字段时，可以通过AS关键字来指定显示别名，比如上述操作可改为：
mysql> SELECT gender AS ‘性别‘,count(gender) AS ‘人数‘
-> FROM stu_info GROUP BY gender;
+--------+--------+
| 性别 | 人数 |
+--------+--------+
| boy | 3 |
| girl | 2 |
+--------+--------+
2 rows in set (0.00 sec)以上是关于mysql存储引擎类型都有哪些的主要内容，如果未能解决你的问题，请参考以下文章