How to use GROUP BY to identify row differences - sql-server

Question

I'm working in SQL Server 2008. I have the following situation. I have a table that has 2 columns which comprise the primary key. (No uniqueness constraint is defined on the key, though.) I know that I have primary key duplicates. Per primary key, I want to identify the distinct values in another column. So, let's say I have the following table:
INSERT INTO some_table (Col1, Col2, COl3) VALUES
('A', '1', 'a'),
('A', '1', 'b'),
('B', '1', 'a'),
('B', '2', 'b'),
('C', '1', 'a'),
('C', '1', 'a'),
('C', '2', 'b')
I want to group by Col1 and Col2, and I want to find all rows where there are more than 1 distinct Col3 values. For example, with the above table, I expect to see:
(A, 1, a), (A, 1, b).
How do I write this SQL query? My SELECT statement needs to include Col1, Col2, and Col3. But, if I do a GROUP BY Col1, Col2, then I can't have Col3 in the SELECT statement.

Answer 1

You can't really have more than one item selected per group in group by, but maybe you need something like this:
select
col1,
col2,
stuff((select ',' + col3 from some_table t2
where t1.col1 = t2.col1 and t1.col2 = t2.col2
FOR XML PATH ('')), 1, 1, '') as items
from
some_table t1
group by
col1,
col2
having count(distinct col3) > 1
This will return the "duplicate" items in comma separated list in the 3rd column.
SQL Fiddle

Answer 2

Here is one way to solve this:
;WITH CTE AS (
Select col1, col2, min(col3) as minvalue, max(col3) as maxvalue
From myTable
Group by col1, col2
Having min(col3) < max(col3)
)
Select *
From myTable t
Inner join cte
On t.col1 = cte.col1
And t.col2 = cte.col2
Where col3 >= minvalue
And col3 <= maxvalue
Note code written directly here, there might be some mistakes.

Answer 3

Try this:
CREATE TABLE #some_table
(
Col1 char(1),
Col2 char(1),
Col3 char(1)
)
INSERT INTO #some_table (Col1, Col2, COl3) VALUES
('A', '1', 'a'),
('A', '1', 'b'),
('B', '1', 'a'),
('B', '2', 'b'),
('C', '1', 'a'),
('C', '1', 'a'),
('C', '2', 'b')
select
stuff((select ',' + '('+Col1 +', '+ Col2 + ', ' + Col3 + ')' from #some_table T_IN
where T.col1 = T_IN.col1 and T.col2 = T_IN.col2 FOR XML PATH ('')), 1, 1, '') as items
from
#some_table T
group by col1, col2

Answer 4

This is one way to get there:
SELECT *
FROM
T T1
WHERE
EXISTS(SELECT * FROM T T2
WHERE
T1.a = T2.a
AND T1.b = T2.b
AND T1.c <> T2.c);
sql fiddle
or in similar variation, that would allow to give the required minimum distinct number:
WHERE
(SELECT COUNT(DISTINCT T2.c)
FROM T T2
WHERE T1.a = T2.a AND T1.b = T2.b) >= 2;
sql fiddle