TSQL：整体计算不同的值并根据组的标准

Question

我有

Groupvar	Subvar	Val
G1	A	x
G1	A	x
G1	B	x
G1	B	y
G1	C	z
G1	C	z
G2	A	x
G2	A	x
G2	B	y
G2	B	z
G2	B	w
G2	C	z

我想要

Groupvar	All count (distinct Val)	A count(distinct Val where Subvar=A)	B count(distinct Val where Subvar=B)	C count(distinct Val where Subvar=C)
G1	3	1	2	1
G2	4	1	3	1

伪代码可以是

    Select 
      Groupvar,
      count(distinct x) as All, 
      count( distinct x where Subvar='A') as A, 
      count( distinct x where Subvar='B') as B, 
      count( distinct x where Subvar='C') as C
    Group by Groupvar

我可以用

    CREATE TABLE #have (
    Groupvar VARCHAR(2),
    Subvar   VARCHAR(1),
    Val VARCHAR(1));
      
    INSERT INTO #have (Groupvar, Subvar, Val )
    VALUES 
        ('G1', 'A', 'x'),   ('G1', 'A', 'x'),   ('G1', 'B', 'x'),   ('G1', 'B', 'y'),   ('G1', 'C', 'z'),   ('G1', 'C', 'z'),
        ('G2', 'A', 'x'),   ('G2', 'A', 'x'),   ('G2', 'B', 'y'),   ('G2', 'B', 'z'),   ('G2', 'B', 'w'),   ('G2', 'C', 'z');
     
    WITH t1 AS (
      SELECT Groupvar, 'All' AS Subvar, COUNT(DISTINCT Val ) AS N_Val FROM #have T1
      GROUP BY Groupvar
      UNION
      SELECT Groupvar, Subvar, COUNT(DISTINCT Val ) AS N_Val FROM #have T1
      GROUP by Groupvar, Subvar
      )
    SELECT * FROM  t1
    PIVOT (SUM(N_Val) FOR Subvar IN([All],[A],[B],[C])) AS pt 

但我想知道是否有一种方法可以在看起来更像我的伪代码示例的单个 select 语句中完成它？

Answer 1

您需要在 COUNT() 聚合函数中使用 CASE 表达式来应用条件聚合：

SELECT Groupvar,
       COUNT(DISTINCT Val) [All], 
       COUNT(DISTINCT CASE WHEN Subvar = 'A' THEN Val END) A, 
       COUNT(DISTINCT CASE WHEN Subvar = 'B' THEN Val END) B, 
       COUNT(DISTINCT CASE WHEN Subvar = 'C' THEN Val END) C
FROM tablename
GROUP BY Groupvar;

参见demo。