SQL：如何检查一列中的每个唯一值可以找到另一列的多少组合

Question

Working in SSMS. Based on a value in one column I want to count the number of different occurrences in another column. How would I go about to do that?

Basically for each unique value in Column 1, how many combinations of Column 2 can be found?

So if table looks like this:

Column 1	Column 2
A	1
A	1
A	1
B	1
B	2
B	3
C	2
C	2
C	3

Desired output would then be:

A = 1

B = 3

C = 2

Answer 1

Use COUNT(DISTINCT) for this case with GROUP BY :

SELECT Col1, COUNT(DISTINCT Col2)
FROM YourTable
GROUP BY Col1

dbfiddle here

Answer 2

WITH CTE(Column1,Column2) AS
(

  SELECT 'A',   1 UNION ALL
  SELECT 'A' ,  1 UNION ALL
  SELECT 'A' ,  1 UNION ALL
  SELECT 'B' ,  1 UNION ALL
  SELECT 'B' ,  2 UNION ALL
  SELECT 'B' ,  3 UNION ALL
  SELECT 'C' ,  2 UNION ALL
  SELECT 'C' ,  2 UNION ALL
  SELECT 'C' ,  3
)
SELECT C.COLUMN1,COUNT(DISTINCT C.COLUMN2)CNTT
 FROM CTE AS C
 GROUP BY C.Column1

CTE is an example you provided. Please replace reference to it with reference to your table