怎么能实现多字段不重复项查询
表示例：
id c1 c2 c3 c4 c5 c6
1 a c f a d d
2 a d f g c a
3 b e g a b r
4 b a g h j e
5 a e c c d q

查询所有c1 - c6 无重复项(a,b,c,d...)的总数目。以及每个项（a,b,c,d...)的出现次数。

[解决办法]

SQL code

 
 --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