I have the following query which have 1000 rows

select 
staffdiscountstartdate,datediff(day,groupstartdate,staffdiscountstartdate),
EmployeeID 
from tblEmployees 
where GroupStartDate < '20100301' and StaffDiscountStartDate > '20100301' 
and datediff(day,groupstartdate,staffdiscountstartdate)>1 
order by staffdiscountstartdate desc

i have the following query which have 400 rows: ie the employees in tblemployees and in tblcards

select a.employeeid,b.employeeid 
from tblEmployees a,tblCards b 
where GroupStartDate < '20100301' 
and StaffDiscountStartDate > '20100301' 
and datediff(day,groupstartdate,staffdiscountstartdate)>1 
and a.employeeid=b.employeeid 

How to list the employees which is there in tblemployees and not in tblcards?

ie is 1000-400 = 600 rows ???