Oracle date如何比较大小分析

-- Created on 2010/04/17 by NAN
declare
-- Local variables here
i integer;
v_date1 DATE;
v_date2 DATE;
begin
-- Test statements here
v_date1 := SYSDATE;
v_date2 := to_date( 2008-09-08);
IF v_date1 > v_date2 THEN
dbms_output.put_line( if);
ELSE
dbms_output.put_line( else);
END IF;
end;