% of open invoices by service month

Service month is =T0.[TaxDate] How can I get the % open by service month. Not sure how I would write this formula. TO.[DocTota], T0.[DocStatus]= '0'/TO.[DocTota],T0.[DocStatus]='C' * 100 From OINV T0

or Select TO.[DocTota],(Sum(Where T0.[DocStatus]= '0'))/ TO.[DocTota],(Sum(Where T0.[DocStatus]= 'C')) * 100 From OINV TO Where To.[TaxDate] = '7/31/2016'