[Xnuiem]

select 
	table1.names
from
	table1		
where
	table1.clv not in (
		select
			table2.clv
		from
			table2,
			table3
		where
			table2.clvp = table3.clvp
			and table3.dat = 'AT-001'
	)
;

Here ya go. It is just a sub select. Now this will not work in MySQL less than 4.1.x