SQL组By/Count：跨多列计数相同的值？

Question

我想弄清楚如何编写一个查询，跨越多个列的计数值，结果表在每列中的每个可能值为列的任何列都有一个计数。

示例：假设我有MYTABLE

Source data table: 

P1 P2 P3 
----------- 
a b a 
a a a 
b b b 
a b b 

我想计数A和B的每列中，产生类似的查询：

Desired query output: 

    P1 P2 P3 
    ------------- 
a | 3 1 2 
b | 1 3 2 

我知道我能做到这一点的单列容易与组通过：

select P1, count(*) as mycounts 
from mytable 
group by P1 

但是是否可以这样做每列？

我正在使用SQL Server 2008（T-SQL）。预先感谢任何帮助！

Answer 1

也许是这样的：

首先是一些测试数据：

DECLARE @tbl TABLE(P1 VARCHAR,P2 VARCHAR,P3 VARCHAR) 

INSERT INTO @tbl 
SELECT 'a','b','a' UNION ALL 
SELECT 'a','a','a' UNION ALL 
SELECT 'b','b','b' UNION ALL 
SELECT 'a','b','b' 

然后枢这样的：

SELECT 
    * 
FROM 
(
    SELECT 'P1' AS P, P1 AS PValue,P1 AS test FROM @tbl 
    UNION ALL 
    SELECT 'P2',P2,P2 FROM @tbl 
    UNION ALL 
    SELECT 'P3',P3,P3 FROM @tbl 
) AS p 
PIVOT 
(
    COUNT(PValue) 
    FOR P IN ([P1],[P2],[P3]) 
) AS pvt 

Here约为透视和逆透视

更多信息

Answer 2

可能不是最有效的，但这个工程。

;WITH data 
AS 
(
    SELECT 'a' AS p1, 'b' AS p2, 'a' AS p3 
    UNION ALL 
    SELECT 'a', 'a','a' 
    UNION ALL 
    SELECT 'b','b','b' 
    UNION ALL 
    SELECT 'a','b','b' 
) 
SELECT 
    p_one.value AS header, 
    p1, 
    p2, 
    p3 
FROM (SELECT 
      p1 AS value, 
      count(*) AS p1 
     FROM data d 
     GROUP BY p1) p_one 
left JOIN (SELECT 
      p2 AS value, 
      count(*) AS p2 
      FROM data d 
      GROUP BY p2) p_two 
    ON p_two.value = p_one.value 
left JOIN (SELECT 
      p3 AS value, 
      count(*) AS p3 
      FROM data d 
      GROUP BY p3) p_three 
    ON p_two.value = p_three.value