By using PL/SQL : You should create and Use this table to help you: Invoice (employee No, customerNo, total price ,invoiceNo,InvoiceDate, branchNo) procedure to add new customer invoice addlnvoice(customername,employeeName, branchName, invoice_date) then the procedure will check from the exists of customername, employee Name, Branch Name by calling there check existsing function for each name and if all of them are exists then a new record will be created with total price equel to zero and the invoceno will be generated using FUNCTION getrextinvoiceNo which return the maximum +1, then the method will display the message " one record has been created with invoice No:show the generated invoice No her in this message " else display a specific message that show the customer or emplovee or branch name doesn't exist please re-enter correct names