Question

Hi Elaine, Thope you are having a nice week! I just wanted to discuss the possibility of receiving some student support for another database related project our company is undertaking. In order to streamline our payroll system, last year we hired an external developer to produce an independent payroll system for our administration staff. Recently however we have been experiencing issues with the backend of the system and would like some help. Below is a basic schema of the system and a sample of some of the data. Employeeſid, firstName, lastName, role] Project[name, description, funding, projectLeader] TimeLog[employeeld, projectName, date, hours Worked, approved] Project.projectLeader references Employee.id TimeLog.employeeld references Employee.id TimeLog.projectName references Project.name

1. The commands have been returning errors however we are unsure whether the issue exists with the UI system or if the commands themselves are incorrect.

2. Would you please be able to help us determine if these operations should be being processed by the backend system and if not, what the error is?

3. using SQL.

Answer 1

Primary key of table Employee is column 'id'

Primary key of table Project is column 'name'

Primary key of table Timelog is composite key (employeeId,projectName,date)

The given queries cannot be executed successfuly because of the following reasons.

a Primary key Foreignkey Employee [id, firstName, Jast Name, rde] - Bumary key Agject [ nome dokouption, funding, preglect leda] Timelog employeeld, pigect Name, date houdhonited, oppoved7 Bumary key © Update tuple <"Website Setup", "Giet a functional webate setup 12000, 2019 > to <"Website Sotpub", "Giet a functional website' Setup" 20000, 1919 > in the seletion "Project”. The query us urcorect and con be moduped to : Updete Project s Set manding = 20000 , Pigject leader = 1919 Where' name = 'Website Selipup'; The tuple <2014," Rebecca", " Zhang", "Administrata" Camot be entered un table employee because the prenary key Jr employee table is colunr Id and allicady there escuts a second un table employee with the Bame punay kay 2014. We know that column poject Name is a foreign key ur teble timelog and repences column name in Project. We are trying to update a record on Tumeloo ☺ * .

and the new project Name us 'Overall Marketing and it does not exist in the premay key column of table poject. Therefore this query corde. Be excedited). Updating the excisting tuple to new tuple is not possible 0.0 The tuple Conot be unserled because the Just olumn is left blank, un <, "Test", "Text", Text"> ånd since it is a Alod pumany key Column ut connot be NULL. 9 This second cennet be sol deleted som leble Employee because value 2014 wn the punay koy denn ld of telle Employee is reponced by the tuple <2014, Website Setup', '1/1000', 'true! > Solution is to fast delete the above decod un table Timelorg and ther delete the required tuple so that the foreign kay Cañabant is not' vidated