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：

[root@dbsvr1 ~]# mysql -u root -pEnter password: Welcome to the MySQL monitor.  Commands end with ; or \g.Your MySQL connection id is 9Server 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 itsaffiliates. Other names may be trademarks of their respectiveowners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> 

执行SHOW ENGINES\G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 ENGINES\G*************************** 1. row ***************************      Engine: InnoDB     Support: DEFAULT                              //此存储引擎为默认     Comment: Supports transactions, row-level locking, and foreign keysTransactions: YES          XA: YES  Savepoints: YES*************************** 2. row ***************************      Engine: MRG_MYISAM     Support: YES     Comment: Collection of identical MyISAM tablesTransactions: NO          XA: NO  Savepoints: NO*************************** 3. row ***************************      Engine: MEMORY     Support: YES     Comment: Hash based, stored in memory, useful for temporary tablesTransactions: 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 engineTransactions: NO          XA: NO  Savepoints: NO*************************** 6. row ***************************      Engine: CSV     Support: YES     Comment: CSV storage engineTransactions: NO          XA: NO  Savepoints: NO*************************** 7. row ***************************      Engine: ARCHIVE     Support: YES     Comment: Archive storage engineTransactions: NO          XA: NO  Savepoints: NO*************************** 8. row ***************************      Engine: PERFORMANCE_SCHEMA     Support: YES     Comment: Performance SchemaTransactions: NO          XA: NO  Savepoints: NO*************************** 9. row ***************************      Engine: FEDERATED     Support: NO                             //此引擎不被支持     Comment: Federated MySQL storage engineTransactions: NULL          XA: NULL  Savepoints: NULL9 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：

[root@dbsvr1 ~]# vim /etc/my.cnf[mysqld].. ..default_storage_engine=MEMORY                              //改用MEMORY引擎[root@dbsvr1 ~]# systemctl  restart mysqld.service           //重启服务

重新登入 mysql> 确认修改结果：

[root@dbsvr1 ~]# mysql -u root -pEnter password: Welcome to the MySQL monitor.  Commands end with ; or \g.Your MySQL connection id is 3Server 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 itsaffiliates. Other names may be trademarks of their respectiveowners.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> exitBye

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：

[root@dbsvr1 ~]# vim /etc/my.cnf[mysqld].. ..default_storage_engine=InnoDB[root@dbsvr1 ~]# 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）：

[root@dbsvr1 ~]# 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：

[root@dbsvr1 ~]# 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：

[root@dbsvr1 ~]# mysql -u root -pEnter password:Welcome to the MySQL monitor.  Commands end with ; or \g.Your MySQL connection id is 5Server 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 itsaffiliates. Other names may be trademarks of their respectiveowners.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 statementmysql> 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：

[root@dbsvr1 ~]#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 '\n'，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'\n'，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: 0

2）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

[root@dbsvr1 ~]# 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'\n' 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：

[root@dbsvr1 ~]# wc -l /var/lib/mysql-files/ulist.txt24 /var/lib/mysql-files/ulist.txt

查看/var/lib/mysql-files/ulist.txt文件的最后10行内容：

[root@dbsvr1 ~]# tail /var/lib/mysql-files/ulist.txt19:avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin24:rpc:x:32:32:Rpcbind Daemon:/var/lib/rpcbind:/sbin/nologin25:rpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologin28:radvd:x:75:75:radvd user:/:/sbin/nologin29:ntp:x:38:38::/etc/ntp:/sbin/nologin33:gdm:x:42:42::/var/lib/gdm:/sbin/nologin35:postfix:x:89:89::/var/spool/postfix:/sbin/nologin36:sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin37:tcpdump:x:72:72::/:/sbin/nologin39:mysql:x:27:27:MySQL Server:/var/lib/mysql:/bin/false

3 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：

[root@dbsvr1 ~]# mysql -uroot -pEnter password: Welcome to the MySQL monitor.  Commands end with ; or \g.Your MySQL connection id is 19Server 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 itsaffiliates. Other names may be trademarks of their respectiveowners.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 namesYou can turn off this feature to get a quicker startup with -ADatabase changedmysql> 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：

[root@dbsvr1 ~]# mysql -u root -pEnter password:Welcome to the MySQL monitor.  Commands end with ; or \g.Your MySQL connection id is 5Server 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 itsaffiliates. Other names may be trademarks of their respectiveowners.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 namesYou can turn off this feature to get a quicker startup with -ADatabase 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)