SELECT
    invoice.invoice_id,
    IF(invoice.paid=0,'unbilled',IF(invoice.paid=1,'paid','unpaid')) AS status,
    IF(invoice.paid=0,'dark-red',IF(invoice.paid=1,'dark-green','light-red')) AS status_colour,
    ROUND(tk.fee*IFNULL(SUM(TIME_TO_SEC(TIMEDIFF(IF(tt.end_time='0000-00-00 00:00:00',now(),tt.end_time), tt.start_time)))/3600,0),2) AS project_fee,
    
    ROUND(SUM(TIME_TO_SEC(TIMEDIFF(IF(tt.end_time='0000-00-00 00:00:00',now(),tt.end_time), tt.start_time)))/3600,2) AS project_hours,
    
    due_days,
    paid
    

FROM

    invoice
    LEFT JOIN invoice_task ON invoice.invoice_id = invoice_task.invoice_id
    LEFT JOIN tasks AS tk ON invoice_task.task_id = tk.task_id
    LEFT JOIN time_tracker AS tt ON tt.element_id = tk.task_id AND tt.element_type=2
    
        ##sql_restrict##

GROUP BY invoice.invoice_id
   
   

   




LIMIT ##limiter##