Show me first names of all customers that have invoice totals less than 20.
select firstname from customer except select t1.lastname from customer as t1 join invoice as t2 on t1.customerid = t2.customerid where t2.total < 20
I meant last names.
select lastname from customer except select t1.lastname from customer as t1 join invoice as t2 on t1.customerid = t2.customerid where t2.total < 20
Oh I meant invoice totals larger than 20, not less than.
select lastname from customer except select t1.lastname from customer as t1 join invoice as t2 on t1.customerid = t2.customerid where t2.total > 20