记录中不同列的计数

Question

如何计算记录的不同列值

  C1   C2     C3    C4
  1  USER1  USER2  USER3
  2  USER1  USER1  USER2
  3  USER2  USER3  USER3
  4  USER1  USER1  USER1 

输出：

 C1   COUNT
  1     3
  2     2 
  3     2
  4     1

如何计算每条记录中的不同用户数。除了比较列值之外，还有其他方法。

感谢。

Answer 1

一种方法是unpivot：

select c1, count(distinct col) as cnt from (
    select * from your_table
    unpivot( col for lst in(C2, C3, C4) )
) tt
group by c1

Answer 2

只有三个比较列，这是最简单的方法：

with cte as (
    select c1, c2 from your_table
    union
    select c1, c3 from your_table
    union   
    select c1, c4 from your_table
)
select c1, count(c2) as cnt
from cte
group by c1
/

union运算符生成一个不同的集合，该集合将输入到聚合计数中。

Answer 3

with cte as (
    select c1, c2 from your_table
    union all
    select c1, c3 from your_table
    union all  
    select c1, c4 from your_table
)
select c1, count(c2) as cnt,count(distinct c2) as distinct_cnt
from cte
group by c1
/