SELECT sum(total) FROM invoices WHERE billing_city  =  "Chicago" AND billing_state  =  "IL";
List total amount of  invoice from Chicago, IL.
SELECT sum ( total ) FROM invoices WHERE billing_city = `` Chicago '' AND billing_state = `` IL '' ;
select sum ( total ) from invoices where billing_city = value and billing_state = value
List total amount of invoice from Chicago , IL .