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NSD DBA DAY02

案例1：常用函数
案例2：查询结果处理
案例3：管理表记录

1 案例1：常用函数

1.1 问题

练习字符函数
练习数学函数
练习日期函数
练习聚集函数
练习数学计算
练习if函数
练习case函数

1.2 方案

函数：MySQL服务内置命令

语法：函数名(表头名)

select格式:

SELECT 函数(表头名) FROM 库名.表名；
SELECT 函数(表头名) FROM 库名.表名 WHERE 条件；

tarena库下的employees表保存133个员工的信息如图-1，图-2

查看tarena库employees表的表头

图-1

查看tarena库employees表表记录

员工编号姓名入职日期出生日期电子邮箱电话号码部门编号

图-2

tarena库下的salary表保存2015以后的工资信息如图-3，图-4

图-3

图-4

行号发工资日期员工编号基本工资奖金

1.3 步骤

实现此案例需要按照如下步骤进行。

步骤一：练习字符函数(处理字符或字符类型的表头)

//LENGTH(str) 返字符串长度，以字节为单位
mysql> select name from tarena.user where name = "root" ;
+------+
| name |
+------+
| root |
+------+
1 row in set (0.00 sec)
mysql> select name , length(name) as 字节个数from tarena.user where name = "root" ;
+------+--------------+
| name | 字节个数 |
+------+--------------+
| root | 4 |
+------+--------------+
1 row in set (0.00 sec)
//一个汉字3个字节
mysql> select name , length(name) from tarena.employees where employee_id = 3 ;
+-----------+--------------+
| name | length(name) |
+-----------+--------------+
| 李玉英 | 9 |
+-----------+--------------+
//CHAR_LENGTH(str) 返回字符串长度，以字符为单位
mysql> select name from tarena.employees where employee_id = 3 ;
+-----------+
| name |
+-----------+
| 李玉英 |
+-----------+
1 row in set (0.00 sec)
mysql> select name , char_length(name) from tarena.employees where employee_id = 3 ;
+-----------+-------------------+
| name | char_length(name) |
+-----------+-------------------+
| 李玉英 | 3 |
+-----------+-------------------+
1 row in set (0.00 sec)
//UPPER(str)和UCASE(str) 将字符串中的字母全部转换成大写
mysql> select name from tarena.user where uid <= 3 ;
+--------+
| name |
+--------+
| root |
| bin |
| daemon |
| adm |
+--------+
4 rows in set (0.00 sec)
mysql> select upper(name) from tarena.user where uid <= 3 ;
+-------------+
| upper(name) |
+-------------+
| ROOT |
| BIN |
| DAEMON |
| ADM |
+-------------+
4 rows in set (0.00 sec)
mysql> select ucase(name) from tarena.user where uid <= 3 ;
+-------------+
| ucase(name) |
+-------------+
| ROOT |
| BIN |
| DAEMON |
| ADM |
+-------------+
4 rows in set (0.00 sec)
//LOWER(str)和LCASE(str) 将str中的字母全部转换成小写
mysql> select lower("ABCD") ;
+---------------+
| lower("ABCD") |
+---------------+
| abcd |
+---------------+
1 row in set (0.00 sec)
mysql> select lcase("ABCD") ;
+---------------+
| lcase("ABCD") |
+---------------+
| abcd |
+---------------+
1 row in set (0.00 sec)
mysql>
//SUBSTR(s, start,end) 从s的start位置开始取出到end长度的子串
mysql> select name from tarena.employees where employee_id <= 3 ;
+-----------+
| name |
+-----------+
| 梁伟 |
| 郭岩 |
| 李玉英 |
+-----------+
3 rows in set (0.00 sec)
//不是输出员工的姓只输出名字
mysql> select substr(name,2,3) from tarena.employees where employee_id <= 3 ;
+------------------+
| substr(name,2,3) |
+------------------+
| 伟 |
| 岩 |
| 玉英 |
+------------------+
3 rows in set (0.00 sec)
//INSTR(str,str1) 返回str1参数，在str参数内的位置
mysql> select name from tarena.user where uid <= 3 ;
+--------+
| name |
+--------+
| root |
| bin |
| daemon |
| adm |
+--------+
4 rows in set (0.00 sec)
mysql> select instr(name,"a") from tarena.user where uid <= 3 ;
+-----------------+
| instr(name,"a") |
+-----------------+
| 0 |
| 0 |
| 2 |
| 1 |
+-----------------+
4 rows in set (0.00 sec)
//查找名字里有英字及出现的位置
mysql> select name , instr(name,"英") from tarena.employees;
+-----------+-------------------+
| name | instr(name,"英") |
+-----------+-------------------+
| 梁伟 | 0 |
| 郭岩 | 0 |
| 李玉英 | 3 |
| 张健 | 0 |
| 郑静 | 0 |
| 牛建军 | 0 |
| 刘斌 | 0 |
| 汪云 | 0 |
| 张建平 | 0 |
| 郭娟 | 0 |
| 郭兰英 | 3 |
| 王英 | 2 |
//TRIM(s) 返回字符串s删除了两边空格之后的字符串
mysql> select trim(" ABC ");
+-----------------+
| trim(" ABC ") |
+-----------------+
| ABC |
+-----------------+
1 row in set (0.00 sec)
mysql>

步骤二：练习数学函数(处理数字或数值类型的表头)

命令操作如下所示：

//ABS(x) 返回x的绝对值
mysql> select abs(11);
+---------+
| abs(11) |
+---------+
| 11 |
+---------+
1 row in set (0.00 sec)
mysql> select abs(-11);
+----------+
| abs(-11) |
+----------+
| 11 |
+----------+
1 row in set (0.00 sec)
mysql>
//PI() 返回圆周率π，默认显示6位小数
mysql> select pi() ;
+----------+
| pi() |
+----------+
| 3.141593 |
+----------+
1 row in set (0.00 sec)
//MOD(x,y) 返回x被y除后的余数
mysql> select mod(10,3);
+-----------+
| mod(10,3) |
+-----------+
| 1 |
+-----------+
1 row in set (0.00 sec)
//输出1-10之间的偶数uid号
mysql> select name , uid from tarena.user where uid between 1 and 10 and mod(uid,2) = 0 ;
+----------+------+
| name | uid |
+----------+------+
| daemon | 2 |
| lp | 4 |
| shutdown | 6 |
| mail | 8 |
+----------+------+
4 rows in set (0.00 sec)
//CEIL(x)、CEILING(x) 返回不小于x的最小整数 (x 是小数)
mysql> select ceil(9.23);
+------------+
| ceil(9.23) |
+------------+
| 10 |
+------------+
1 row in set (0.00 sec)
mysql> select ceiling(9.23);
+---------------+
| ceiling(9.23) |
+---------------+
| 10 |
+---------------+
1 row in set (0.00 sec)
mysql>
//FLOOR(x）返回不大于x的最大整数 (x 是有小数的数字)
mysql> select floor(9.23);
+-------------+
| floor(9.23) |
+-------------+
| 9 |
+-------------+
1 row in set (0.00 sec)

步骤三：练习日期函数 (获取系统或指定的日期与时间)

图-5

命令操作如下所示：

mysql> select curtime(); //获取系统时间
+-----------+
| curtime() |
+-----------+
| 17:42:20 |
+-----------+
1 row in set (0.00 sec)
mysql> select curdate();//获取系统日期
+------------+
| curdate() |
+------------+
| 2023-05-24 |
+------------+
1 row in set (0.00 sec)
mysql> select now() ;//获取系统日期+时间
+---------------------+
| now() |
+---------------------+
| 2023-05-24 17:42:29 |
+---------------------+
1 row in set (0.00 sec)
mysql> select year(now()) ; //获取系统当前年
+-------------+
| year(now()) |
+-------------+
| 2023 |
+-------------+
1 row in set (0.00 sec)
mysql> select month(now()) ; //获取系统当前月
+--------------+
| month(now()) |
+--------------+
| 5 |
+--------------+
1 row in set (0.00 sec)
mysql> select day(now()) ; //获取系统当前日
+------------+
| day(now()) |
+------------+
| 24 |
+------------+
1 row in set (0.00 sec)
mysql> select hour(now()) ; //获取系统当前小时
+-------------+
| hour(now()) |
+-------------+
| 17 |
+-------------+
1 row in set (0.00 sec)
mysql> select minute(now()) ; //获取系统当分钟
+---------------+
| minute(now()) |
+---------------+
| 46 |
+---------------+
1 row in set (0.00 sec)
mysql> select second(now()) ; //获取系统当前秒
+---------------+
| second(now()) |
+---------------+
| 34 |
+---------------+
1 row in set (0.00 sec)
mysql> select time(now()) ;//获取当前系统时间
+-------------+
| time(now()) |
+-------------+
| 17:47:36 |
+-------------+
1 row in set (0.00 sec)
mysql> select date(now()) ; //获取当前系统日期
+-------------+
| date(now()) |
+-------------+
| 2023-05-24 |
+-------------+
1 row in set (0.00 sec)
mysql> select curdate();//获取当前系统日志
+------------+
| curdate() |
+------------+
| 2023-05-24 |
+------------+
1 row in set (0.00 sec)
mysql> select dayofmonth(curdate());//获取一个月的第几天
+-----------------------+
| dayofmonth(curdate()) |
+-----------------------+
| 24 |
+-----------------------+
1 row in set (0.00 sec)
mysql> select dayofyear(curdate());//获取一年中的第几天
+----------------------+
| dayofyear(curdate()) |
+----------------------+
| 144 |
+----------------------+
1 row in set (0.00 sec)
mysql>
mysql> select monthname(curdate());//获取月份名
+----------------------+
| monthname(curdate()) |
+----------------------+
| May |
+----------------------+
1 row in set (0.00 sec)
mysql> select dayname(curdate());//获取星期名
+--------------------+
| dayname(curdate()) |
+--------------------+
| Wednesday |
+--------------------+
1 row in set (0.00 sec)
mysql> select quarter(curdate());//获取一年中的第几季度
+--------------------+
| quarter(curdate()) |
+--------------------+
| 2 |
+--------------------+
1 row in set (0.00 sec)
mysql> select week(now());//一年中的第几周
+-------------+
| week(now()) |
+-------------+
| 21 |
+-------------+
1 row in set (0.00 sec)
mysql> select weekday(now())；//一周中的周几
+----------------+
| weekday(now()) |
+----------------+
| 2 |
+----------------+
1 row in set (0.00 sec)

步骤四：练习聚集函数(对数值类型表头下的数据做统计)

命令操作如下所示：

输出3号员工2018每个月的基本工资

mysql> select basic from tarena.salary where employee_id=3 and year(date)=2018;
+-------+
| basic |
+-------+
| 9261 |
| 9261 |
| 9261 |
| 9261 |
| 9261 |
| 9261 |
| 9261 |
| 9261 |
| 9261 |
| 9261 |
| 9261 |
| 9724 |
+-------+
12 rows in set (0.00 sec)

sum(表头名) 求和

mysql> select sum(basic) from tarena.salary where employee_id=3 and year(date)=2018;
+------------+
| sum(basic) |
+------------+
| 111595 |
+------------+
1 row in set (0.00 sec)

avg(表头名) 计算平均值

mysql> select avg(basic) from tarena.salary where employee_id=3 and year(date)=2018;
+------------+
| avg(basic) |
+------------+
| 9299.5833 |
+------------+
1 row in set (0.00 sec)

min(表头名) 获取最小值

mysql> select min(basic) from tarena.salary where employee_id=3 and year(date)=2018;
+------------+
| min(basic) |
+------------+
| 9261 |
+------------+
1 row in set (0.00 sec)

max(表头名) 获取最大值

mysql> select max(basic) from tarena.salary where employee_id=3 and year(date)=2018;
+------------+
| max(basic) |
+------------+
| 9724 |
+------------+
1 row in set (0.00 sec)

count(表头名) 统计表头值个数

//输出3号员工2018年奖金小于3000的奖金
mysql> select bonus from tarena.salary where employee_id=3 and year(date)=2018 and bonus<3000;
+-------+
| bonus |
+-------+
| 1000 |
| 1000 |
| 1000 |
+-------+
3 rows in set (0.00 sec)
//统计3号员工2018年奖金小于3000的次数
mysql> select count(bonus) from tarena.salary where employee_id=3 and year(date)=2018 and bonus<3000;
+--------------+
| count(bonus) |
+--------------+
| 3 |
+--------------+
1 row in set (0.01 sec)

步骤五：练习数学计算对行中的列做计算

图-6

命令操作如下所示：

输出8号员工2019年1月10 工资总和

mysql> select employee_id ,date , basic + bonus as 总工资 from tarena.salary
where employee_id = 8 and date=20190110;
+-------------+------------+----------------+
| employee_id | date | 总工资 |
+-------------+------------+----------------+
| 8 | 2019-01-10 | 24093 |
+-------------+------------+----------------+

输出8号员工的名字和年龄

mysql> select name , 2022 - year(birth_date) as 年龄 from tarena.employees
where employee_id = 8 ;
+--------+--------+
| name | 年龄 |
+--------+--------+
| 汪云 | 29 |
+--------+--------+

查看8号员工2019年1月10 基本工资翻3倍的值

mysql> select employee_id , basic , basic * 3 as 工资翻三倍 from tarena.salary
where employee_id=8 and date=20190110;
+-------------+-------+-----------------+
| employee_id | basic | 工资翻三倍 |
+-------------+-------+-----------------+
| 8 | 23093 | 69279 |
+-------------+-------+-----------------+
1 row in set (0.00 sec)

查看8号员工2019年1月10的平均工资

mysql> select employee_id , (basic+bonus)/2 as 平均工资 from tarena.salary where employee_id=8 and date=20190110 ;
+-------------+--------------+
| employee_id | 平均工资 |
+-------------+--------------+
| 8 | 12046.5000 |
+-------------+--------------+
1 row in set (0.01 sec)

输出员工编号1-10之间偶数员工编号及对应的员工名

mysql> select employee_id , name from tarena.employees
where employee_id between 1 and 10 and employee_id % 2 = 0 ;
+-------------+-----------+
| employee_id | name |
+-------------+-----------+
| 2 | 郭岩 |
| 4 | 张健 |
| 6 | 牛建军 |
| 8 | 汪云 |
| 10 | 郭娟 |
+-------------+-----------+
5 rows in set (0.00 sec)

步骤六：练习if函数

if(条件,v1,v2) 如果条件是TRUE则返回v1，否则返回v2

ifnull(v1,v2) 如果v1不为NULL，则返回v1，否则返回v2

演示if（）语句的执行过程

mysql> select if(1 = 2 , "a","b");
+---------------------+
| if(1 = 2 , "a","b") |
+---------------------+
| b |
+---------------------+
1 row in set (0.00 sec)
mysql> select if( 1 = 1 , "a","b");
+---------------------+
| if(1 = 1 , "a","b") |
+---------------------+
| a |
+---------------------+
1 row in set (0.00 sec)
mysql>

演示ifnull（）语句的执行过程

mysql> select ifnull("abc","xxx");
+---------------------+
| ifnull("abc","xxx") |
+---------------------+
| abc |
+---------------------+
1 row in set (0.00 sec)
mysql> select ifnull(null,"xxx");
+--------------------+
| ifnull(null,"xxx") |
+--------------------+
| xxx |
+--------------------+
1 row in set (0.00 sec)
mysql>

查询例子

根据uid 号输出用户类型

mysql> select name , uid ,
#cold_boldif(uid < 1000 , "系统用户","创建用户") as 用户类型 from tarena.user;
+-----------------+-------+--------------+
| name | uid | 用户类型 |
+-----------------+-------+--------------+
| root | 0 | 系统用户 |
| bin | 1 | 系统用户 |
| daemon | 2 | 系统用户 |
| adm | 3 | 系统用户 |
| lp | 4 | 系统用户 |
| sync | 5 | 系统用户 |
| shutdown | 6 | 系统用户 |
| halt | 7 | 系统用户 |
| mail | 8 | 系统用户 |
| operator | 11 | 系统用户 |
| games | 12 | 系统用户 |
| ftp | 14 | 系统用户 |
| nobody | 99 | 系统用户 |
| systemd-network | 192 | 系统用户 |
| dbus | 81 | 系统用户 |
| polkitd | 999 | 系统用户 |
| sshd | 74 | 系统用户 |
| postfix | 89 | 系统用户 |
| chrony | 998 | 系统用户 |
| rpc | 32 | 系统用户 |
| rpcuser | 29 | 系统用户 |
| nfsnobody | 65534 | 创建用户 |
| haproxy | 188 | 系统用户 |
| plj | 1000 | 创建用户 |
| apache | 48 | 系统用户 |
| mysql | 27 | 系统用户 |
| bob | NULL | 创建用户 |
+-----------------+-------+--------------+
27 rows in set (0.00 sec)

根据shell 输出用户类型

mysql> select name , shell ,
#cold_boldif(shell = "/bin/bash" , "交互用户","非交户用户") as 用户类型 from tarena.user;
+-----------------+----------------+-----------------+
| name | shell | 用户类型 |
+-----------------+----------------+-----------------+
| root | /bin/bash | 交互用户 |
| bin | /sbin/nologin | 非交户用户 |
| daemon | /sbin/nologin | 非交户用户 |
| adm | /sbin/nologin | 非交户用户 |
| lp | /sbin/nologin | 非交户用户 |
| sync | /bin/sync | 非交户用户 |
| shutdown | /sbin/shutdown | 非交户用户 |
| halt | /sbin/halt | 非交户用户 |
| mail | /sbin/nologin | 非交户用户 |
| operator | /sbin/nologin | 非交户用户 |
| games | /sbin/nologin | 非交户用户 |
| ftp | /sbin/nologin | 非交户用户 |
| nobody | /sbin/nologin | 非交户用户 |
| systemd-network | /sbin/nologin | 非交户用户 |
| dbus | /sbin/nologin | 非交户用户 |
| polkitd | /sbin/nologin | 非交户用户 |
| sshd | /sbin/nologin | 非交户用户 |
| postfix | /sbin/nologin | 非交户用户 |
| chrony | /sbin/nologin | 非交户用户 |
| rpc | /sbin/nologin | 非交户用户 |
| rpcuser | /sbin/nologin | 非交户用户 |
| nfsnobody | /sbin/nologin | 非交户用户 |
| haproxy | /sbin/nologin | 非交户用户 |
| plj | /bin/bash | 交互用户 |
| apache | /sbin/nologin | 非交户用户 |
| mysql | /bin/false | 非交户用户 |
| bob | NULL | 非交户用户 |
+-----------------+----------------+-----------------+
27 rows in set (0.00 sec)

插入没有家目录的用户

mysql> insert into tarena.user (name, homedir) values ("jerrya",null);

查看时加判断

mysql> select name 姓名, ifnull(homedir,"NO home")as 家目录 from tarena.user;
+-----------------+--------------------+
| 姓名 | 家目录 |
+-----------------+--------------------+
| root | /root |
| bin | /bin |
| daemon | /sbin |
| adm | /var/adm |
| lp | /var/spool/lpd |
| sync | /sbin |
| shutdown | /sbin |
| halt | /sbin |
| mail | /var/spool/mail |
| operator | /root |
| games | /usr/games |
| ftp | /var/ftp |
| nobody | / |
| systemd-network | / |
| dbus | / |
| polkitd | / |
| sshd | /var/empty/sshd |
| postfix | /var/spool/postfix |
| chrony | /var/lib/chrony |
| rpc | /var/lib/rpcbind |
| rpcuser | /var/lib/nfs |
| nfsnobody | /var/lib/nfs |
| haproxy | /var/lib/haproxy |
| plj | /home/plj |
| apache | /usr/share/httpd |
| mysql | /var/lib/mysql |
| bob | NO home |
| jerrya | NO home |
+-----------------+--------------------+
28 rows in set (0.00 sec)
Mysql>

步骤七：练习case函数

命令格式

CASE 表头名
WHEN 值1 THEN 输出结果
WHEN 值2 THEN 输出结果
WHEN 值3 THEN 输出结果
ELSE 输出结果
END
或
CASE
WHEN 判断条件1 THEN 输出结果
WHEN 判断条件2 THEN 输出结果
WHEN 判断条件3 THEN 输出结果
ELSE 输出结果
END

如果表头名等于某个值，则返回对应位置then后面的值并结束判断，

如果与所有值都不相等，则返回else后面的结果并结束判断

命令操作如下所示：

查看部门表(departments)所有行

mysql> select * from tarena.departments;
+---------+-----------+
| dept_id | dept_name |
+---------+-----------+
| 1 | 人事部 |
| 2 | 财务部 |
| 3 | 运维部 |
| 4 | 开发部 |
| 5 | 测试部 |
| 6 | 市场部 |
| 7 | 销售部 |
| 8 | 法务部 |
+---------+-----------+
8 rows in set (0.03 sec)
//输出部门类型
select dept_id, dept_name,
case dept_name
when '运维部' then '技术部门'
when '开发部' then '技术部门'
when '测试部' then '技术部门'
else '非技术部门'
end as 部门类型 from tarena.departments;
+---------+-----------+-----------------+
| dept_id | dept_name | 部门类型 |
+---------+-----------+-----------------+
| 1 | 人事部 | 非技术部门 |
| 2 | 财务部 | 非技术部门 |
| 3 | 运维部 | 技术部门 |
| 4 | 开发部 | 技术部门 |
| 5 | 测试部 | 技术部门 |
| 6 | 市场部 | 非技术部门 |
| 7 | 销售部 | 非技术部门 |
| 8 | 法务部 | 非技术部门 |
+---------+-----------+-----------------+
8 rows in set (0.00 sec)
或
mysql> select dept_id,dept_name,
-> case
-> when dept_name="运维部" then "技术部"
-> when dept_name="开发部" then "技术部"
-> when dept_name="测试部" then "技术部"
-> else "非技术部"
-> end as 部门类型 from tarena.departments;
+---------+-----------+--------------+
| dept_id | dept_name | 部门类型 |
+---------+-----------+--------------+
| 1 | 人事部 | 非技术部 |
| 2 | 财务部 | 非技术部 |
| 3 | 运维部 | 技术部 |
| 4 | 开发部 | 技术部 |
| 5 | 测试部 | 技术部 |
| 6 | 市场部 | 非技术部 |
| 7 | 销售部 | 非技术部 |
| 8 | 法务部 | 非技术部 |
+---------+-----------+--------------+
8 rows in set (0.00 sec)
或
mysql> select dept_id,dept_name,
-> case
-> when dept_name in ("运维部","开发部","测试部") then "技术部"
-> else "非技术部"
-> end as 部门类型 from tarena.departments;
+---------+-----------+--------------+
| dept_id | dept_name | 部门类型 |
+---------+-----------+--------------+
| 1 | 人事部 | 非技术部 |
| 2 | 财务部 | 非技术部 |
| 3 | 运维部 | 技术部 |
| 4 | 开发部 | 技术部 |
| 5 | 测试部 | 技术部 |
| 6 | 市场部 | 非技术部 |
| 7 | 销售部 | 非技术部 |
| 8 | 法务部 | 非技术部 |
+---------+-----------+--------------+
8 rows in set (0.00 sec)

2 案例2：查询结果处理

2.1 问题

分组练习
排序练习
过滤练习
分页练习

2.2 方案

使用tarena库下的表完成练习

对select语句查找到的数据再做处理，语法格式

SELECT 表头名 FROM 库名.表名 [WHERE条件] 分组 | 排序 | 过滤 | 分页;

2.3 步骤

实现此案例需要按照如下步骤进行。

步骤一：分组练习

命令操作如下所示：

输出符合条件的shell 和 name

mysql> select shell , name from tarena.user where shell in ("/bin/bash","/sbin/nologin");
+---------------+-----------------+
| shell | name |
+---------------+-----------------+
| /bin/bash | root |
| /sbin/nologin | bin |
| /sbin/nologin | daemon |
| /sbin/nologin | adm |
| /sbin/nologin | lp |
| /sbin/nologin | mail |
| /sbin/nologin | operator |
| /sbin/nologin | games |
| /sbin/nologin | ftp |
| /sbin/nologin | nobody |
| /sbin/nologin | systemd-network |
| /sbin/nologin | dbus |
| /sbin/nologin | polkitd |
| /sbin/nologin | sshd |
| /sbin/nologin | postfix |
| /sbin/nologin | chrony |
| /sbin/nologin | rpc |
| /sbin/nologin | rpcuser |
| /sbin/nologin | nfsnobody |
| /sbin/nologin | haproxy |
| /bin/bash | plj |
| /sbin/nologin | apache |
+---------------+-----------------+
22 rows in set (0.00 sec)

统计每种解释器用户的个数（按照shell表头值分组统计name表头值个数）

mysql> select shell as 解释器 , count(name) as 总人数 from tarena.user where shell in ("/bin/bash","/sbin/nologin") group by shell;
+---------------+-----------+
| 解释器 | 总人数 |
+---------------+-----------+
| /bin/bash | 2 |
| /sbin/nologin | 20 |
+---------------+-----------+
2 rows in set (0.00 sec)

统计每个部门的总人数 (按照部门表头分组统计name表头值的个数)

mysql> select dept_id , count(name) from tarena.employees group by dept_id ;
+---------+-------------+
| dept_id | count(name) |
+---------+-------------+
| 1 | 8 |
| 2 | 5 |
| 3 | 6 |
| 4 | 55 |
| 5 | 12 |
| 6 | 9 |
| 7 | 35 |
| 8 | 3 |
+---------+-------------+
8 rows in set (0.00 sec)

步骤二：排序练习

命令操作如下所示：

查看满足条件记录的name和uid 字段的值

mysql> select name , uid from tarena.user where uid is not null and uid between 100 and 1000 ;
+-----------------+------+
| name | uid |
+-----------------+------+
| systemd-network | 192 |
| polkitd | 999 |
| chrony | 998 |
| haproxy | 188 |
| plj | 1000 |
+-----------------+------+
5 rows in set (0.00 sec)

按照uid升序排序

mysql> select name , uid from tarena.user where uid is not null and uid between 100 and 1000 order by uid asc;
+-----------------+------+
| name | uid |
+-----------------+------+
| haproxy | 188 |
| systemd-network | 192 |
| chrony | 998 |
| polkitd | 999 |
| plj | 1000 |
+-----------------+------+
5 rows in set (0.00 sec)

按照uid降序排序

mysql> select name , uid from tarena.user where uid is not null and uid between 100 and 1000 order by uid desc;
+-----------------+------+
| name | uid |
+-----------------+------+
| plj | 1000 |
| polkitd | 999 |
| chrony | 998 |
| systemd-network | 192 |
| haproxy | 188 |
+-----------------+------+
5 rows in set (0.00 sec)

查看2015年1月10号员工编号小于10的工资总额

mysql> select employee_id , date , basic , bonus , basic+bonus as total from tarena.salary where date=20150110 and employee_id <= 10;
+-------------+------------+-------+-------+-------+
| employee_id | date | basic | bonus | total |
+-------------+------------+-------+-------+-------+
| 2 | 2015-01-10 | 17000 | 10000 | 27000 |
| 3 | 2015-01-10 | 8000 | 2000 | 10000 |
| 4 | 2015-01-10 | 14000 | 9000 | 23000 |
| 6 | 2015-01-10 | 14000 | 10000 | 24000 |
| 7 | 2015-01-10 | 19000 | 10000 | 29000 |
+-------------+------------+-------+-------+-------+
5 rows in set (0.00 sec)

以工资总额升序排，总额相同按照员工编号升序排

mysql> select employee_id , basic+bonus as total from tarena.salary where date=20150110 and employee_id <= 10 order by total asc ,employee_id asc;
+-------------+-------+
| employee_id | total |
+-------------+-------+
| 3 | 10000 |
| 4 | 23000 |
| 6 | 24000 |
| 2 | 27000 |
| 7 | 29000 |
+-------------+-------+
5 rows in set (0.00 sec)

步骤三：过滤练习

在查找到的数据里过滤符合条件的数据。

select 表头名 from 库.表 where 筛选条件 having 筛选条件;

命令操作如下所示：

查找部门总人数少于10人的部门名称及人数

//第一步，查看所有员工的部门名称
select dept_id , name from tarena.employees;
//第二步，按部门编号分组统计人名个数
mysql> select dept_id , count(name) as numbers from tarena.employees group by dept_id;
+---------+---------+
| dept_id | numbers |
+---------+---------+
| 1 | 8 |
| 2 | 5 |
| 3 | 6 |
| 4 | 55 |
| 5 | 12 |
| 6 | 9 |
| 7 | 35 |
| 8 | 3 |
+---------+---------+
8 rows in set (0.00 sec)
//第三步，查找部门人数少于10人的部门名称及人数
mysql> select dept_id , count(name) as numbers from tarena.employees group by dept_id having numbers < 10;
+---------+---------+
| dept_id | numbers |
+---------+---------+
| 1 | 8 |
| 2 | 5 |
| 3 | 6 |
| 6 | 9 |
| 8 | 3 |
+---------+---------+
5 rows in set (0.00 sec)

步骤四：分页练习

分析：

作用：限制查询结果显示行数（默认显示全部查询结果）

使用SELECT查询时，如果结果集数据量很大，比如1万行数据，放在一个页面显示的话数据量太大，可以分100次显示每次只显示100行。

语法:

SELECT语句 LIMIT 数字; //显示查询结果前多少条记录
SELECT语句 LIMIT 数字1,数字2; //显示指定范围内的查询记录
数字1 表示起始行（0表示第1行）数字2表示总行数

例如：

limit 1 ; 显示查询结果的第1行
limit 3 ; 显示查询结果的前3行
limit 10 ; 显示查询结果的前10行
limit 0,1 ; 从查询结果的第1行开始显示，共显示1行
limit 3,5 ; 从查询结果的第4行开始显示，共显示5行
limit 10,10; 从查询结果的第11行开始显示，共显示10行

命令操作如下所示：

查看有解释器的用户信息

mysql> select * from tarena.user where shell is not null ;

只显示查询结果的第1行

mysql> select * from tarena.user where shell is not null limit 1;

只显示查询结果的前3行

mysql> select * from tarena.user where shell is not null limit 3;

仅仅显示查询结果的第1行到第3 （0 表示查询结果的第1行）

mysql> select * from user where shell is not null limit 0,3;

从查询结果的第4行开始显示，共显示3行

mysql> select name,uid , gid , shell from user where shell is not null limit 3,3;

查看uid 号最大的用户名和UID

mysql> select name , uid from tarena.user order by uid desc limit 1 ;
+-----------+-------+
| name | uid |
+-----------+-------+
| nfsnobody | 65534 |
+-----------+-------+
1 row in set (0.00 sec)

3 案例3：管理表记录

3.1 问题

练习插入表记录
练习修改表记录
练习删除表记录

3.2 方案

使用tarena库下的user表完成表记录管理的练习。

3.3 步骤

实现此案例需要按照如下步骤进行。

步骤一：练习插入表记录

命令操作如下所示：

查看表头

mysql> desc tarena.user;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| name | char(20) | YES | | NULL | |
| password | char(1) | YES | | NULL | |
| uid | int | YES | | NULL | |
| gid | int | YES | | NULL | |
| comment | varchar(50) | YES | | NULL | |
| homedir | varchar(80) | YES | | NULL | |
| shell | char(30) | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
8 rows in set (0.00 sec)

插入1条记录给所有表头赋值

（给所有表头赋值表头可以省略不写）id表头的值不能重复，主键的知识在后边课程里讲

mysql> insert into tarena.user values(40,"jingyaya","x",1001,1001,"teacher","/home/jingyaya","/bin/bash");
Query OK, 1 row affected (0.05 sec)

查看表记录

mysql> select * from tarena.user where name="jingyaya";
+----+----------+----------+------+------+---------+----------------+-----------+
| id | name | password | uid | gid | comment | homedir | shell |
+----+----------+----------+------+------+---------+----------------+-----------+
| 40 | jingyaya | x | 1001 | 1001 | teacher | /home/jingyaya | /bin/bash |
+----+----------+----------+------+------+---------+----------------+-----------+
1 row in set (0.00 sec)
mysql>

插入多行记录给所有列赋值

insert into tarena.user values
(41,"jingyaya2","x",1002,1002,"teacher","/home/jingyaya2","/bin/bash"),
(42,"jingyaya3","x",1003,1003,"teacher","/home/jingyaya3","/bin/bash");

插入1行给指定列赋值，必须写列名，没赋值的列没有数据后通过设置的默认值赋值

mysql> insert into tarena.user(name,uid,shell)values("benben",1002,"/sbin/nologin");

插入多行给指定列赋值，必须写列名，没赋值的列没有数据后通过设置的默认值赋值

mysql> insert into tarena.user(name,uid,shell)values("benben2",1002,"/sbin/nologin"),("benben3",1003,"/sbin/nologin");

查看记录

mysql> select * from tarena.user where name like "benben%";
+----+---------+----------+------+------+---------+---------+---------------+
| id | name | password | uid | gid | comment | homedir | shell |
+----+---------+----------+------+------+---------+---------+---------------+
| 41 | benben | NULL | 1002 | NULL | NULL | NULL | /sbin/nologin |
| 42 | benben2 | NULL | 1002 | NULL | NULL | NULL | /sbin/nologin |
| 43 | benben3 | NULL | 1003 | NULL | NULL | NULL | /sbin/nologin |
+----+---------+----------+------+------+---------+---------+---------------+
3 rows in set (0.00 sec)

使用select查询结果赋值(查询表头个数和插入记录命令表头个数要一致)

mysql> select user from mysql.user;
+------------------+
| user |
+------------------+
| mysql.infoschema |
| mysql.session |
| mysql.sys |
| root |
+------------------+
4 rows in set (0.00 sec)
mysql> insert into tarena.user(name) (select user from mysql.user);
Query OK, 4 rows affected (0.09 sec)
Records: 4 Duplicates: 0 Warnings: 0

查看插入后的数据

mysql> select * from tarena.user where name like "mysql%" or name="root";
+----+------------------+----------+------+------+--------------+----------------+------------+
| id | name | password | uid | gid | comment | homedir | shell |
+----+------------------+----------+------+------+--------------+----------------+------------+
| 1 | root | x | 0 | 0 | root | /root | /bin/bash |
| 26 | mysql | x | 27 | 27 | MySQL Server | /var/lib/mysql | /bin/false |
| 44 | mysql.infoschema | NULL | NULL | NULL | NULL | NULL | NULL |
| 45 | mysql.session | NULL | NULL | NULL | NULL | NULL | NULL |
| 46 | mysql.sys | NULL | NULL | NULL | NULL | NULL | NULL |
| 47 | root | NULL | NULL | NULL | NULL | NULL | NULL |
+----+------------------+----------+------+------+--------------+----------------+------------+
6 rows in set (0.00 sec)

使用set命令赋值

mysql> insert into tarena.user set name="yaya" , uid=99 , gid=99 ;
Query OK, 1 row affected (0.06 sec)
mysql> select * from tarena.user where name="yaya";
+----+------+----------+------+------+---------+---------+-------+
| id | name | password | uid | gid | comment | homedir | shell |
+----+------+----------+------+------+---------+---------+-------+
| 28 | yaya | NULL | 99 | 99 | NULL | NULL | NULL |
+----+------+----------+------+------+---------+---------+-------+
1 row in set (0.00 sec)

步骤二：练习修改表记录

命令操作如下所示：

//修改前查看
mysql> select name , comment from tarena.user where id <= 10 ;
+----------+----------+
| name | comment |
+----------+----------+
| root | root |
| bin | bin |
| daemon | daemon |
| adm | adm |
| lp | lp |
| sync | sync |
| shutdown | shutdown |
| halt | halt |
| mail | mail |
| operator | operator |
+----------+----------+
10 rows in set (0.00 sec)
//修改符合条件
mysql> update tarena.user set comment=NULL where id <= 10 ;
Query OK, 10 rows affected (0.09 sec)
Rows matched: 10 Changed: 10 Warnings: 0
//修改后查看
mysql> select name , comment from tarena.user where id <= 10 ;
+----------+---------+
| name | comment |
+----------+---------+
| root | NULL |
| bin | NULL |
| daemon | NULL |
| adm | NULL |
| lp | NULL |
| sync | NULL |
| shutdown | NULL |
| halt | NULL |
| mail | NULL |
| operator | NULL |
+----------+---------+
10 rows in set (0.00 sec) [root@localhost ~]#
//修改前查看
mysql> select name , homedir from tarena.user;
+------------------+--------------------+
| name | homedir |
+------------------+--------------------+
| root | /root |
| bin | /bin |
| daemon | /sbin |
| adm | /var/adm |
| lp | /var/spool/lpd |
| sync | /sbin |
| shutdown | /sbin |
| halt | /sbin |
| mail | /var/spool/mail |
| operator | /root |
| games | /usr/games |
| ftp | /var/ftp |
| nobody | / |
| systemd-network | / |
| dbus | / |
| polkitd | / |
| sshd | /var/empty/sshd |
| postfix | /var/spool/postfix |
| chrony | /var/lib/chrony |
| rpc | /var/lib/rpcbind |
| rpcuser | /var/lib/nfs |
| nfsnobody | /var/lib/nfs |
| haproxy | /var/lib/haproxy |
| plj | /home/plj |
| apache | /usr/share/httpd |
| mysql | /var/lib/mysql |
| bob | NULL |
| jerrya | NULL |
| jingyaya | /home/jingyaya |
| benben | NULL |
| benben2 | NULL |
| benben3 | NULL |
| mysql.infoschema | NULL |
| mysql.session | NULL |
| mysql.sys | NULL |
| root | NULL |
+------------------+--------------------+
36 rows in set (0.00 sec)
//不加条件批量修改
mysql> update tarena.user set homedir="/student" ;
Query OK, 36 rows affected (0.09 sec)
Rows matched: 36 Changed: 36 Warnings: 0
//修改后查看
mysql> select name , homedir from tarena.user;
+------------------+----------+
| name | homedir |
+------------------+----------+
| root | /student |
| bin | /student |
| daemon | /student |
| adm | /student |
| lp | /student |
| sync | /student |
| shutdown | /student |
| halt | /student |
| mail | /student |
| operator | /student |
| games | /student |
| ftp | /student |
| nobody | /student |
| systemd-network | /student |
| dbus | /student |
| polkitd | /student |
| sshd | /student |
| postfix | /student |
| chrony | /student |
| rpc | /student |
| rpcuser | /student |
| nfsnobody | /student |
| haproxy | /student |
| plj | /student |
| apache | /student |
| mysql | /student |
| bob | /student |
| jerrya | /student |
| jingyaya | /student |
| benben | /student |
| benben2 | /student |
| benben3 | /student |
| mysql.infoschema | /student |
| mysql.session | /student |
| mysql.sys | /student |
| root | /student |
+------------------+----------+
36 rows in set (0.00 sec)

步骤三：练习删除表记录

命令操作如下所示：

//删除前查看
mysql> select * from tarena.user where id <= 10 ;
+----+----------+----------+------+------+---------+----------+----------------+
| id | name | password | uid | gid | comment | homedir | shell |
+----+----------+----------+------+------+---------+----------+----------------+
| 1 | root | x | 0 | 0 | NULL | /student | /bin/bash |
| 2 | bin | x | 1 | 1 | NULL | /student | /sbin/nologin |
| 3 | daemon | x | 2 | 2 | NULL | /student | /sbin/nologin |
| 4 | adm | x | 3 | 4 | NULL | /student | /sbin/nologin |
| 5 | lp | x | 4 | 7 | NULL | /student | /sbin/nologin |
| 6 | sync | x | 5 | 0 | NULL | /student | /bin/sync |
| 7 | shutdown | x | 6 | 0 | NULL | /student | /sbin/shutdown |
| 8 | halt | x | 7 | 0 | NULL | /student | /sbin/halt |
| 9 | mail | x | 8 | 12 | NULL | /student | /sbin/nologin |
| 10 | operator | x | 11 | 0 | NULL | /student | /sbin/nologin |
+----+----------+----------+------+------+---------+----------+----------------+
10 rows in set (0.00 sec)
//仅删除与条件匹配的行
mysql> delete from tarena.user where id <= 10 ;
Query OK, 10 rows affected (0.06 sec)
//查不到符合条件的记录了
mysql> select * from tarena.user where id <= 10 ;
Empty set (0.00 sec)