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SQL Server数据库入门教程之多表查询

作者：M malloc

这篇文章主要给大家介绍了关于SQL Server数据库入门教程之多表查询的相关资料,多表查询是SQL数据库里的高级查询语句,文中通过图文以及实例代码介绍的非常详细,需要的朋友可以参考下

SQL_Server的前情介绍

😁大家好呀，今天是我第三次写sql_server，也是最近才学习sql_server，也想着记录一下自己的学习过程，并且分享给大家尼！

一、sql_server技术介绍

SQL Server 是由微软公司（Microsoft）开发的关系型数（RDBMS）。RDBMS 是 SQL 以及所有现代数据库系统的基础，比如 MS SQL Server，IBM DB2，Oracle，MySQL 以及微软的 Microsoft Access。

二、学习前的准备工作

编程软件：SQL Server Management Studio 2012
带好你的小板凳，我们一起扬帆起航！

SQL_Server之多表查询

笛卡尔乘积的讲解

在数据库中有一种叫笛卡尔乘积其语法如下：

select * from People,Department

此查询结果会将People表的所有数据和Department表的所有数据进行依次排列组合形成新的记录。例如People表有10条记录，Department表有3条记录，则排列组合之后查询结果会有10*3=30条记录.

多表查询

接下来我们来看几个例子吧！

1.查询员工信息，显示部门信息

select * from People,department where People.DepartmentId = department.DepartmentId

2.查询员工信息，显示职级名称

select * from People,s_rank where People.RankId = s_rank.RankId

3.查询员工信息，显示部门名称，显示职级名称

select * from People,department,s_rank 
	where People.departmentId = department.DepartmentId and People.RankId = s_rank.RankId

内连接查询

在数据库的查询过程中，存在有内连接查询，这个时候，我们就需要用到inner这个关键字，下面我们来看几个例子吧！

1.查询员工信息，显示部门信息

select * from People inner join department on People.departmentId = department.DepartmentId

2.查询员工信息，显示职级名称

select * from People inner join s_rank on People.RankId = s_rank.RankId

3.查询员工信息，显示部门名称，显示职级名称

select * from People inner join department on People.departmentId = department.DepartmentId
inner join s_rank on People.RankId = s_rank.RankId

外连接查询(左外连，右外连，全外连)

1.查询员工信息，显示部门信息(左外连)

select * from People left join department on People.departmentId = department.DepartmentId

2.查询员工信息，显示职级名称(左外接)

select * from People left join s_rank on People.RankId = s_rank.RankId

3.查询员工信息，显示部门名称，显示职级名称(左外连)

select * from People left join department on People.departmentId = department.DepartmentId
inner join s_rank on People.RankId = s_rank.RankId

4.右外连

A left join B = B right join A

select * from People right join department on People.departmentId = department.DepartmentId

全外连查询(无论是否符合关系，都要显示数据)

1.select * from People full join department on People.departmentId = department.DepartmentId

多表查询的主要例子

1.查询出武汉地区所有的员工信息，要求显示部门名称，以及员工的详细资料（显示中文别名）

select PeopleId 员工编号,DepartmentName 部门名称,PeopleName 员工姓名,PeopleSex 员工性别,
PeopleBirth 员工生日,PeoPleSalary 月薪,PeoplePhone 电话,PeopleAddress 地址
from People,department where People.departmentId = department.DepartmentId

2.查询出武汉地区所有员工的信息，要求显示部门名称，职级名称以及员工的详细资料

select PeopleId 员工编号,DepartmentName 部门名称,RankName 职级名称, PeopleName 员工姓名,PeopleSex 员工性别,
PeopleBirth 员工生日,PeoPleSalary 月薪,PeoplePhone 电话,PeopleAddress 地址
from People,department,s_rank where People.departmentId = department.DepartmentId 
and People.RankId = s_rank.RankId and PeopleAddress = '武汉'

3.根据部门分组统计员工人数，员工工资总和，平均工资，最高工资和最低工资

select DepartmentName 部门名称, count(*) 员工人数,sum(PeopleSalary) 工资总和,avg(PeopleSalary) 平均工资,max(PeopleSalary) 最高工资,min(PeopleSalary) 最低工资 
from People,department
	where People.departmentId = department.DepartmentId
		group by department.DepartmentId,DepartmentName

4.根据部门分组统计员工人数，员工工资总和，平均工资，最高工资和最低工资平均工资在10000元以下的不参与排序。根据平均工资降序排序

select DepartmentName 部门名称, count(*) 员工人数,sum(PeopleSalary) 工资总和,avg(PeopleSalary) 平均工资,max(PeopleSalary) 最高工资,min(PeopleSalary) 最低工资 
from People,department
	where People.departmentId = department.DepartmentId 
		group by department.DepartmentId,DepartmentName	
			having avg(PeopleSalary) >= 15000 
				order by avg(PeopleSalary) desc

5.根据部门名称，然后根据职位名称分组，统计员工人数，员工工资总和
平均工资，最高工资，和最低工资

select DepartmentName 部门名称,RankName 职级名称, count(*) 员工人数,sum(PeopleSalary) 工资总和,avg(PeopleSalary) 平均工资,max(PeopleSalary) 最高工资,min(PeopleSalary) 最低工资 
from People,department,s_rank
	where People.departmentId = department.DepartmentId and People.RankId = s_rank.RankId
		group by department.DepartmentId,DepartmentName,s_rank.RankId,s_rank.RankName

如何巩固学习

提示：在学习的过程中，我们需要先自行进行思考，而不是一遇到不会的就放弃思考直接看答案，如果最后遇到真的不会的题目，我们可以适当的进行观看答案，看自己的思路是否正确，在作出正确的判断

总结

到此这篇关于SQL Server数据库入门教程之多表查询的文章就介绍到这了,更多相关SQLServer多表查询内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！

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