sql - SQL 中的透视/反透视

Question

我通过分析表中的值生成了一个 SQL 视图，以便该字段包含值“N”、“D”或“V”。我可以按列计算总数，但不能按行计算……这可能吗？

例子：

数据

No, Col_1, Col_2, Col_3

 1,     N,     N,     N

 2,     N,     D,     D

 3,     N,     V,     D

 4,     V,     V,     V

我如何总结第 3 行有 1N、1V 和 3ds 而第 4 行有 4Vs？

赌注很简单，但遗憾的是我也是！

非常感谢，彼得

Answer 1

 select case when col_1 = 'N' then 1 else 0 end as n_count from tablename;

概括为：

 select 
   case when col_1 = 'N' then 1 else 0 end 
   + case when col_2 = 'N' then 1 else 0 end 
   + case when col_2 = 'N' then 1 else 0 end as n_count,
   case when col_1 = 'V' then 1 else 0 end 
   + case when col_2 = 'V' then 1 else 0 end 
   + case when col_2 = 'V' then 1 else 0 end as v_count,
   ....
  from tablename;

Answer 2

怎么样？

select no,
sum(case when val = 'N' then 1 else 0 end) ncnt,
sum(case when val = 'V' then 1 else 0 end) vcnt,
sum(case when val = 'D' then 1 else 0 end) dcnt from
(select no, col_1 val from t union all 
 select no, col_2 from t union all
 select no, col_3 from t)
group by no
order by no