Concatenation - T-SQL

Question

I have the following so far.

DECLARE @Table Table (ID int, Value1 varchar(50), Value2 varchar(50), Value3 varchar(50))
INSERT INTO @Table (ID, Value1, Value2, Value3)
SELECT 1, 'One', 'Uno', 'FIrst'
UNION ALL
SELECT 2, 'Two', 'Dos', 'Second'
UNION ALL
SELECT 3, 'One', 'Uno', 'Third'
UNION ALL
SELECT 4, 'Three', 'Tres', 'Fourth'

SELECT *, CASE
            WHEN COUNT(*) OVER (PARTITION BY  Value1, Value2) > 1 THEN 1
            ELSE 0
        END AS Duplicate  FROM @Table

Which gives me duplicate. I want to derive one more column which would have concatenated value for the duplicate records as 'First - Third' (both columns)

Expected output

ID  Value1  Value2  Value3  Duplicate   Value3
1   One     Uno     FIrst   1           First - Third
3   One     Uno     Third   1           First - Third
4   Three   Tres    Fourth  0           NULL
2   Two     Dos     Second  0           NULL 

Answer 1

Unfortunately, SQL Server doesn't have aggregate concatenation function, but you can use xml trick:

select
   t.ID, t.Value1, t.Value2, t.Value3,
   case
       when count(*) over(partition by t.Value1, t.Value2) > 1 then 1
       else 0
   end as Duplicate,
   stuff(
       (
          select ' - ' + TT.Value3
          from @Table as TT
          where TT.Value1 = t.Value1 and TT.Value2 = t.Value2
          for xml path(''), type
       ).value('.', 'nvarchar(max)')
   , 1, 3, '') as Value3_Dupl
from @Table as t

sql fiddle demo

If you need to show duplicates only for Duplicate = 1 , I think it's better to use cte (or subquery), it's a bit cleaner:

;with cte as (
    select *, count(*) over(partition by Value1, Value2) as cnt
    from @Table
)
select
   t.ID, t.Value1, t.Value2, t.Value3,
   case
       when cnt > 1 then 1
       else 0
   end as Duplicate,
   case
       when cnt > 1 then
         stuff(
             (
                select ' - ' + TT.Value3
                from @Table as TT
                where TT.Value1 = t.Value1 and TT.Value2 = t.Value2
                for xml path(''), type
             ).value('.', 'nvarchar(max)')
         , 1, 3, '')
    end as Value3_Dupl
from cte as t

sql fiddle demo

And just quick note - I'm using type after for xml path('') and then taking concatenated string with value('.', 'nvarchar(max)') function, and this is not just because I like it. If you don't use solutin this way, and just use implicit conversion to varchar , the characters like '<' or '&' will not be converted properly.

Answer 2

SELECT *, 
    CASE
        WHEN COUNT(*) OVER (PARTITION BY  Value1, Value2) > 1 THEN 1
        ELSE 0
    END AS Duplicate, 

    CASE WHEN COUNT(*) OVER (PARTITION BY  Value1, Value2) > 1 
        THEN STUFF((SELECT ' - ' + Value3 
                    FROM @Table T 
                    WHERE T.Value1 = V.Value1 
                    AND T.Value2 = V.Value2 
                    FOR XML PATH('')), 
                   1, 3, '')
        ELSE NULL 
    END
FROM @Table V

SQL Fiddle Example

Answer 3

TRY THIS ONE:

DECLARE @Table Table (ID int, Value1 varchar(50), Value2 varchar(50), Value3 varchar(50))
INSERT INTO @Table (ID, Value1, Value2, Value3)
SELECT 1, 'One', 'Uno', 'FIrst'
UNION ALL
SELECT 2, 'Two', 'Dos', 'Second'
UNION ALL
SELECT 3, 'One', 'Uno', 'Third'
UNION ALL
SELECT 4, 'Three', 'Tres', 'Fourth'


;WITH CTE_MY
AS
(
SELECT *, 
CASE
    WHEN COUNT(*) OVER (PARTITION BY  Value1, Value2) > 1 THEN 1
    ELSE 0
END AS Duplicate
FROM @Table
)

DECLARE @Table Table (ID int, Value1 varchar(50), Value2 varchar(50), Value3 varchar(50))
INSERT INTO @Table (ID, Value1, Value2, Value3)
SELECT 1, 'One', 'Uno', 'FIrst'
UNION ALL
SELECT 2, 'Two', 'Dos', 'Second'
UNION ALL
SELECT 3, 'One', 'Uno', 'Third'
UNION ALL
SELECT 4, 'Three', 'Tres', 'Fourth'


;WITH CTE_MY
AS
(
SELECT *, 
CASE
    WHEN COUNT(*) OVER (PARTITION BY  Value1, Value2) > 1 THEN 1
    ELSE 0
END AS Duplicate
FROM @Table
)

SELECT *, 
CASE WHEN (SELECT CAST(M1.Value3 AS VARCHAR(MAX)) + ' - ' +CAST(M2.Value3 AS VARCHAR(MAX)) FROM CTE_MY M2 WHERE M1.Value1 = M2.Value1 AND M1.ID <> M2.ID) = 'Third - FIrst' THEN 'FIrst - Third' ELSE 
(SELECT CAST(M1.Value3 AS VARCHAR(MAX)) + ' - ' +CAST(M2.Value3 AS VARCHAR(MAX)) FROM CTE_MY M2 WHERE M1.Value1 = M2.Value1 AND M1.ID <> M2.ID) END VALUE3
FROM CTE_MY M1