Is there a way to do the following? I get a invTotal column not found.

	Select invoice.cCompanyName,  ;
		sum(invoice.yTotal) as invTotal,  ;
		sum(invoice.ySalesTax) as invTax,  ;
		invTotal - invTax as netRev  ;
		from invoice  ;
		group by cCompanyName ;

- or do I have to do -

	Select invoice.cCompanyName,  ;
		sum(invoice.yTotal) as invTotal,  ;
		sum(invoice.ySalesTax) as invTax,  ;
		sum(invoice.yTotal) - sum(invoice.ySalesTax) as netRev  ;</b>
		from invoice  ;
		group by cCompanyName ;