I do not know which table to use here all the tables

Pls use oracle Pl/sql command line

The system must contain tables such as category(catNo ,catogeryName) ,Items(itemNo,ItemName,Price,total_quantity, catNo), Items_stor_entry(entry_no number primary key,itemNo,entry_date ,quantity),

Employee (employeeNo,employeeName,job) ,branch(No,Name), Customer(customerNo,costomerName,gender) ,

,Invoice (employeeNo,customerNo,total price ,invoiceNo,InvoiceDate,branchNo )

InvoiceDeatail contain List Of Purchase Items contain detail information related to the invoice (invoiceNo,ItemNo, paidPrice, quantity) . create getItemTotalPrice function which to return quantity*paidPrice

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- Method to add new Employee which use validation method checkExistingEmployee using cursor to validate Employee name if its not exists before, then add this Employee and generate the Employee number automatically using database trigger.