--无重复项(a,b,c,d...)的总数目 
 select count(*) 
 from(select c1 from table 
 union  
 select c2 from table 
 union  
 select c3 from table 
 union  
 select c4 from table 
 union  
 select c5 from table 
 union  
 select c6 from table) as T  
  
  
 --每个项（a,b,c,d...)的出现次数 
 select c1,count(*) 
 from(select c1 from table 
 union all 
 select c2 from table 
 union all 
 select c3 from table 
 union all 
 select c4 from table 
 union all 
 select c5 from table 
 union all 
 select c6 from table) as T  
 group by c1