一个关于时间的问题

Question

select *  from web where datediff(dd,2009-06-01 , shijian)>0

Answer 1

select *  from web where datediff(dd,'2009-06-01' , shijian)>0

Answer 2

select *  from web where shijian > '2009-06-01' 
select *  from web where shijian > '2009-12-01' 

Answer 3

select * from web where datediff(dd,'2009-06-01',shijian)>0
select * from web where datediff(dd,'2009-12-01',shijian)>0
select *  from web where shijian > '2009-06-01' 
select *  from web where shijian > '2009-12-01'