如何在sql中添加天数时排除周末

I have the following tables on oracle DB PRB_phases which contains: PRBID,CREATION_DATE,INSERTIONDATE,ENDDATE,PRIORITY,COMPLEXITY,PHASES and table RFQ_HOLD_TIME which contains RFQID,HOLDDATE,UNHOLDDATE where i save the time that the problem is on hold status so on the following query except the information about the problem also calculate the result of holdtime and add it to the "phase"deadline but i want to exclude the weekend when add days for deadline phases an also when add time to deadline from the holdtime. I have the following tables on oracle DB PRB_ph