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,
    
    DATE_FORMAT(invoice.sent_date,'%d/%m/%Y') AS sent_date,
    DATE_FORMAT(DATE_ADD( sent_date, INTERVAL due_days DAY ),'%d/%m/%Y') AS due_date,
    datediff(now(),DATE_ADD( sent_date, INTERVAL due_days DAY )) AS date_diff,
    ct.client_name,
    pt.project_name

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
    ,
    client_table AS ct,
    projects AS pt
    
WHERE

    DATE_ADD( sent_date, INTERVAL due_days DAY ) < now( )
    AND invoice.paid='2'
    AND ct.client_id = invoice.client_id
    AND pt.project_id = invoice.project_id

GROUP BY invoice.invoice_id

LIMIT ##limiter##