create table #tab(sn int identity,sl int,aa varchar(10)) 
  
 insert into #tab(sl) select 5 union all select 8 union all select 10 union all select 25 union all select 30 
  
  
 select a.*,convert(float,a.sl)*100/b.sum_sl 'sl%' from #tab a,(select sum_sl=sum(sl) from #tab) b  
 where (select sum(sl) from (select a.sn,convert(float,a.sl)*100/b.sum_sl sl from #tab a,(select sum_sl=sum(sl) from #tab) b) c where c.sn <=a.sn) <=80 
  
 --结果 
 sn      sl      aa     sl%                            
 ----------- ----------- ---------- -----------------------------------------------------  
 1       5       NULL     6.4102564102564106 
 2       8       NULL     10.256410256410257 
 3       10      NULL     12.820512820512821 
 4       25      NULL     32.051282051282051 
  
 （所影响的行数为 4 行）