做个判断，忘

做个判断，忘高手指点！
做个if判断，条件是      
select   sdate   from   songinfo   where   datediff(dd,sdate,getdate())> 0  
如果条件成立，它执行“update   songinfo   set   dayhit=1”；
不成立的话，执行select   *   from   songinfo   ;
SQL语句怎么写？？？


------解决方案--------------------
if exists (select sdate from songinfo where datediff(dd,sdate,getdate())> 0)
update songinfo set dayhit=1

else
select * from songinfo