SQL grouping

Question

I have a table with the following columns:

A   B   C
---------
1   10  X
1   11  X
2   15  X
3   20  Y
4   15  Y
4   20  Y

I want to group the data based on the B and C columns and count the distinct values of the A column. But if there are two ore more rows where the value on the A column is the same I want to get the maximum value from the B column.

If I do a simple group by the result would be:

B   C    Count
--------------
10  X    1
11  X    1
15  X    1
20  Y    2
15  Y    1

What I want is this result:

B   C    Count
--------------
11  X    1
15  X    1
20  Y    2

Is there any query that can return this result. Server is SQL Server 2005.

Answer 1

I like to work in steps: first get rid of duplicate A records, then group. Not the most efficient, but it works on your example.

with t1 as (
    select A, max(B) as B, C 
        from YourTable
        group by A, C
)
select count(A) as CountA, B, C
    from t1
    group by B, C

Answer 2

I have actually tested this:

SELECT 
    MAX( B ) AS B,
    C,
    Count 
FROM
(
    SELECT
        B, C, COUNT(DISTINCT A) AS Count
    FROM
        t
    GROUP BY
    B, C
) X
GROUP BY C, Count

and it gives me:

 B     C     Count    
 ----  ----  -------- 
 15    X     1        
 15    y     1        
 20    y     2        

Answer 3

Check this out. This should work in Oracle, although I haven't tested it;

select count(a), BB, CC from
(
select a, max(B) BB, Max(C) CC
from yourtable
group by a
)
group by BB,CC

Answer 4

WITH cteA AS 
(
    SELECT 
        A, C, 
        MAX(B) OVER(PARTITION BY A, C) [Max]
    FROM T1
)

SELECT 
    [Max] AS B, C, 
    COUNT(DISTINCT A) AS [Count]
FROM cteA
GROUP BY C, [Max];