SELECT

    IF(invoice.paid=0,'unbilled',IF(invoice.paid=1,'paid','unpaid')) AS status,
    IFNULL(SUM(tasks.task_hours),0) AS project_hours,
    IFNULL(FORMAT(SUM(tasks.fee),2),0) AS project_fee
    

FROM

    invoice ,
    tasks ,
    invoice_task 

WHERE

    invoice.project_id = '##project_id##'
    
    AND invoice.invoice_id = invoice_task.invoice_id
    AND invoice_task.task_id = tasks.task_id
    
    
GROUP BY invoice.paid