291 lines
9.4 KiB
Markdown
291 lines
9.4 KiB
Markdown
# 综合案例3——数据表查询操作
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SQL语句可以分为两部分，一部分用来创建数据库对象，另一部分用来操作这些对象，本部分内容详细介绍了操作数据库对象的数据表查询语句。通过部分内容的介绍，同学们可以了解到SQL中的查询语言功能的强大，用户可以根据需要灵活使用。此综合案例将回顾这些查询语句。
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## 1、案例目的
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根据不同条件对表进行查询操作，掌握数据表的查询语句。employee、dept表结构以及表中的记录如表1~表4所示。
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表1 employee表结构
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| 字段名 | 数据类型 | 主键 | 外键 | 非空 | 唯一 | 自增 | 字段说明 |
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| -------- | ------------- | ---- | ---- | ---- | ---- | ---- | -------- |
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| e_no | int（11） | 是 | 否 | 是 | 是 | 否 | 员工编号 |
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| e_name | varchar（50） | 否 | 否 | 是 | 否 | 否 | 员工姓名 |
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| e_gender | char（2） | 否 | 否 | 否 | 否 | 否 | 员工性别 |
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| dept_no | int（11） | 否 | 是 | 是 | 否 | 否 | 部门编号 |
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| e_job | varchar（50） | 否 | 否 | 是 | 否 | 否 | 职位 |
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| e_salary | int（11） | 否 | 否 | 是 | 否 | 否 | 薪水 |
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| hiredate | date | 否 | 否 | 是 | 否 | 否 | 入职日期 |
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表2 dept表结构
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| 字段名 | 数据类型 | 主键 | 外键 | 非空 | 唯一 | 自增 | 字段说明 |
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| ---------- | -------------- | ---- | ---- | ---- | ---- | ---- | -------- |
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| d_no | int（11） | 是 | 否 | 是 | 是 | 是 | 部门编号 |
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| d_name | varchar（50） | 否 | 否 | 是 | 否 | 否 | 部门姓名 |
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| d_location | varchar（100） | 否 | 否 | 否 | 否 | 否 | 部门地址 |
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表3 employee表中的记录
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| e_no | e_name | e_gender | dept_no | e_job | e_salary | hiredate |
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| ---- | ------ | -------- | ------- | --------- | -------- | ---------- |
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| 1001 | Smith | m | 20 | clerk | 800 | 2005-11-12 |
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| 1002 | Allen | f | 30 | salesman | 1600 | 2003-05-12 |
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| 1003 | Ward | f | 30 | salesman | 1250 | 2003-05-12 |
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| 1004 | Jones | m | 20 | manager | 2975 | 1998-05-18 |
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| 1005 | Martin | m | 30 | salesman | 1250 | 2001-06-12 |
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| 1006 | Blake | f | 30 | manager | 2850 | 1997-02-15 |
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| 1007 | Clark | m | 10 | manager | 2450 | 2002-09-12 |
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| 1008 | Scott | m | 20 | analyst | 3000 | 2003-05-12 |
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| 1009 | King | f | 10 | president | 5000 | 1995-01-01 |
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| 1010 | Turner | f | 30 | salesman | 1500 | 1997-10-12 |
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| 1011 | Adams | m | 20 | clerk | 1100 | 1999-10-05 |
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| 1012 | James | f | 30 | clerk | 950 | 2008-06-15 |
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表4 dept表中的记录
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| d_no | d_name | d_location |
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| ---- | ---------- | ---------- |
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| 10 | accounting | ShangHai |
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| 20 | research | BeiJing |
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| 30 | sales | ShenZhen |
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| 40 | operations | FuJian |
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## 2、案例操作过程
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（1）登录MySQL数据库。
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```mysql
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mysql -h localhost -u root -p
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```
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截图：
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（2）创建数据库MANGER并选择使用此数据库。
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```mysql
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create database MANGER;
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use MANGER;
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```
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截图：
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（3）按照表1、表2创建表employee和dept，创建成功后用desc查看表结构。
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```mysql
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create table dept(
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d_no int(11) not null unique auto_increment,
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d_name varchar(50) not null,
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d_location varchar(100) null,
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primary key(d_no)
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);
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desc dept;
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```
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```mysql
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create table employee(
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e_no int(11) not null unique,
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e_name varchar(50) not null,
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e_gender char(2) null,
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dept_no int(11) not null,
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e_job varchar(50) not null,
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e_salary int(11) not null,
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hiredate date not null,
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primary key(e_no),
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foreign key (dept_no)references dept(d_no)
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);
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desc employee;
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```
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截图：
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（4）将表3、表4的记录分别插入两个表中。
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```mysql
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insert into dept (d_no,d_name,d_location)
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values(10,'accounting','ShangHai'),
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(20,'research','BeiJing'),
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(30,'sales','ShenZhen'),
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(40,'operations','FuJian');
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```
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```mysql
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insert into employee (e_no,e_name,e_gender,dept_no,e_job,e_salary,hiredate)
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values(1001,'Smith','m',20,'clerk',800,'2005-11-12'),
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(1002,'Allen','f',30,'salesman',1600,'2003-05-12'),
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(1003,'Ward','f',30,'salesman',1250,'2003-05-12'),
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(1004,'Jones','m',20,'manager',2975,'1998-05-18'),
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(1005,'Martin','m',30,'salesman',1250,'2001-06-12'),
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(1006,'Blake','f',30,'manager',2850,'1997-02-15'),
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(1007,'Clark','m',10,'manager',2450,'2002-09-12'),
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(1008,'Scott','m',20,'analyst',3000,'2003-05-12'),
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(1009,'King','f',10,'president',5000,'1995-01-01'),
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(1010,'Turner','f',30,'salesman',1500,'1997-10-12'),
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(1011,'Adams','m',20,'clerk',1100,'1999-10-05'),
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(1012,'James','f',30,'clerk',950,'2008-06-15');
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```
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截图：
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（5）在employee表中，查询所有记录的e_no、e_name和e_salary字段值。
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```mysql
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select e_no,e_name,e_salary from employee;
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```
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截图：
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（6）在employee表中，查询dept_no等于10和20的所有记录。
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```mysql
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select * from employee where dept_no=10 or dept_no=20;
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```
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截图：
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（7）在employee表中，查询工资范围在800~2500之间的员工信息。
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```mysql
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select * from employee where e_salary>=800 and e_salary<=2500;
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```
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截图：
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（8）在employee表中，查询部门编号为20的部门中的员工所有信息。
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```mysql
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select * from employee where dept_no=20;
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```
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截图：
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（9）在employee表中，查询每个部门最高工资的员工信息。
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```mysql
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select *,max(e_salary) from employee group by dept_no;
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```
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截图：
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（10）查询员工Blake所在部门编号和部门所在地。
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```mysql
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select d_name,d_location from dept as de where de.d_no=(select dept_no from employee where e_name='Blake');
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```
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截图：
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（11）使用连接查询，查询所有员工的部门和和部门信息。
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```mysql
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select * from employee as em,dept as de where de.d_no=em.dept_no;
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```
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截图：
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（12）在employee表中，计算每个部门各有多少名员工。
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```mysql
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select count(e_name),dept_no from employee group by dept_no;
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```
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截图：
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（13）在employee表中，计算不同类型职工的总工资数。
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```mysql
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select e_job,sum(e_salary) from employee group by e_job;
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```
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截图：
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（14）在employee表中，计算不同部门的平均工资。
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```mysql
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select dept_no,avg(e_salary) from employee group by dept_no;
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```
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截图：
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（15）在employee表中，查询工资低于1500的员工信息。
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```mysql
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select * from employee where e_salary<1500;
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```
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截图：
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（16）在employee表中，将查询记录先按部门编号由高到低排列，若部门相同再按员工工资由高到低排列。
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```mysql
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select * from employee order by dept_no desc,e_salary desc;
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```
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截图：
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（17）在employee表中，查询员工姓名以字母A或S开头的员工信息。
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```mysql
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select * from employee where e_name like 'A%' or e_name like 'S%';
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```
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截图：
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（18）在employee表中，查询到目前为止，工龄大于等于20年的员工信息。
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```mysql
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select * from employee as em where (select year(now())-(select year(em.hiredate)))>20;
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```
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截图：
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