作业帮请问下面的数据库 关系代数表达式怎么写啊?Employee(EmployeeId,EmployeeName,Block,UnitNo,Street,City)Working(EmployeeId,CompanyId,Salary)Company(CompanyId,CompanyName,City)Managing(EmployeeId,ManagerID)Write relational algebra express
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请问下面的数据库 关系代数表达式怎么写啊?Employee(EmployeeId,EmployeeName,Block,UnitNo,Street,City)Working(EmployeeId,CompanyId,Salary)Company(CompanyId,CompanyName,City)Managing(EmployeeId,ManagerID)Write relational algebra express
请问下面的数据库 关系代数表达式怎么写啊?
Employee(EmployeeId,EmployeeName,Block,UnitNo,Street,City)
Working(EmployeeId,CompanyId,Salary)
Company(CompanyId,CompanyName,City)
Managing(EmployeeId,ManagerID)
Write relational algebra expressions for the following queries:
(1) Find the list of EmployeeIds and EmployeeNames working in the company XYZ.
(2) Find all Employees who live in the same city as the company in which they work.
(3) Find all employees who work for City Bank and earn more than $30000.
(4) Find the number of employees working in each company and the average salary.
请问下面的数据库 关系代数表达式怎么写啊?Employee(EmployeeId,EmployeeName,Block,UnitNo,Street,City)Working(EmployeeId,CompanyId,Salary)Company(CompanyId,CompanyName,City)Managing(EmployeeId,ManagerID)Write relational algebra express
1)查询在XYZ工资工作的员工ID和姓名列表.
SELECT a.EmployeeId,a.EmployeeName
from Employee a,Working b,Company c
where a.EmployeeId = b.EmployeeId
and b.CompanyId = c.CompanyId
and c.CompanyName = 'XYZ'
2)查找居住地和公司所在地在同一个城市的所有员工
select a.EmployeeId,EmployeeName,a.City
from Employee a,Working b,Company c
where a.EmployeeId = b.EmployeeId
and b.CompanyId = c.CompanyId
and a.city = c.city
3)查找在CITY BANK工作并且工资大于30000美金的员工
Select a.EmployeeId,a.EmployeeName,b.Salary
from Employee a,Working b,Company c
where a.EmployeeId = b.EmployeeId
and b.CompanyId = c.CompanyId
and c.CompanyName = 'City Bank'
and b.Salary > 30000
4)查找每个公司员工的人数以及平均工资
SELECT b.CompanyName,COUNT(1) as empcnt,avg(a.salary) as avgsalary
from Working a,Company b
where a.companyid = b.companyid
group by b.companyname