Question

Consider the following database instance, which contains information about employees and the projects to which they are assigned:

Employee

empId	lastName
E101	Smith
E105	Jones
E110	Adams
E115	Smith

Project

projectNo	projectName	budget
P10	Hudson	50000
P15	Columbia	60000
P20	Wabash	40000
P23	Arkansas	80000

Assign

employeeId	projectNo	hours
E101	P10	40
E101	P15	30
E104	P10	20
E110	P15	30
E110	P20	30
E115	P10	20
E115	P20	30

• Show the table that would be produced by each of the following relational algebra commands:

A. SELECT Employee WHERE lastName = ‘Adams’

B. SELECT Project WHERE budget < 70000 GIVING CheapProj
PROJECT ChapProj OVER projectName

C. SELECT Assign WHERE hours > 25 GIVING MuchWork
PROJECT MuchWork OVER employeeId

Answer 1

A. SELECT Employee WHERE lastName = ‘Adams’
The table which will be displayed is
empId lastName
E110 Adams

as we are selecting the entry from the table with all columns where last name is adams

b)SELECT Project WHERE budget < 70000 GIVING CheapProj
the table that will be displayed is

projectNo cheapProject budget
P10 Hudson 50000
P15 Columbia 60000
P20 Wabash 40000

as we are selecting all entries whose budget is less than 70000 and changing the project name column to cheapProject

c)SELECT Assign WHERE hours > 25 GIVING MuchWork
the table that will be displayed is

MuchWork projectNo hours
E101 P10 40
E101 P15 30
E110 P15 30
E110 P20 30
E115 P20 30

as we are selecting all entries that have hours greater than 25, and changing the name of the column employeeId with MuchWork.

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