How to concatenate all strings from a certain column for each group - sql

Question

Suppose I have this table [Table1]
Name Mark
------- ------
ABC 10
DEF 10
GHI 10
JKL 20
MNO 20
PQR 30
What should be my SQL statement to retrieve a record that looks like this:
(group by [mark]).
I have done the 1 and 2 columns but don't know how to accomplish the third column (concat the [name] with the same [mark])
mark count names
---- ----- -----------
10 3 ABC,DEF,GHI
20 2 JKL,MNO
30 1 PQR
I'm using Microsoft SQL.
Please help. Thanks

Answer 1

If MS SQL 2005 or higher.
declare #t table([name] varchar(max), mark int)
insert #t values ('ABC', 10), ('DEF', 10), ('GHI', 10),
('JKL', 20), ('MNO', 20), ('PQR', 30)
select t.mark, COUNT(*) [count]
,STUFF((
select ',' + [name]
from #t t1
where t1.mark = t.mark
for xml path(''), type
).value('.', 'varchar(max)'), 1, 1, '') [values]
from #t t
group by t.mark
Output:
mark count values
----------- ----------- --------------
10 3 ABC,DEF,GHI
20 2 JKL,MNO
30 1 PQR

Answer 2

Here's a performance-related answer!
http://jerrytech.blogspot.com/2010/04/tsql-concatenate-strings-1-2-3-and.html
Using XML functions in a large query is a performance killer.
Using a CTE is a performance superstar.
Check out the link, it will explain how.
I admit the work to accomplish it is more.
But the result is milliseconds over millions of rows.

Answer 3

polishchuks solution is more elegant, but this is basically the same thing, we just deal with the trailing comma differently.
CREATE TABLE #Marks(Name nchar(3), Mark int)
INSERT INTO #Marks
SELECT 'ABC', 10 UNION ALL
SELECT 'DEF', 10 UNION ALL
SELECT 'GHI', 10 UNION ALL
SELECT 'JKL', 20 UNION ALL
SELECT 'MNO', 20 UNION ALL
SELECT 'PQR', 30
SELECT
mark,
[count],
CASE WHEN Len(Names) > 0 THEN LEFT(Names, LEN(Names) -1) ELSE '' END names
FROM
(
SELECT
Mark,
COUNT(Mark) AS [count],
(
SELECT DISTINCT
Name + ', '
FROM
#Marks M1
WHERE M1.Mark = M2.Mark
FOR XML PATH('')
) Names
FROM #Marks M2
GROUP BY Mark
) M

Answer 4

Loosely based on Itzik Ben-Gan, Inside Microsoft SQL Server 2005: T-SQL Programming, p. 215:
IF OBJECT_ID('dbo.Table1') IS NOT NULL
DROP TABLE dbo.Table1 ;
GO
CREATE TABLE dbo.Table1 ( Name VARCHAR(10), Mark INT ) ;
INSERT INTO dbo.Table1 ( Name, Mark ) VALUES ( 'ABC', 10 ) ;
INSERT INTO dbo.Table1 ( Name, Mark ) VALUES ( 'DEF', 10 ) ;
INSERT INTO dbo.Table1 ( Name, Mark ) VALUES ( 'GHI', 10 ) ;
INSERT INTO dbo.Table1 ( Name, Mark ) VALUES ( 'JKL', 20 ) ;
INSERT INTO dbo.Table1 ( Name, Mark ) VALUES ( 'MNO', 20 ) ;
INSERT INTO dbo.Table1 ( Name, Mark ) VALUES ( 'PQR', 30 ) ;
WITH DelimitedNames AS
(
SELECT Mark, T2.Count,
( SELECT Name + ',' AS [text()]
FROM dbo.Table1 AS T1
WHERE T1.Mark = T2.Mark
ORDER BY T1.Mark
FOR XML PATH('')) AS Names
FROM ( SELECT Mark, COUNT(*) AS Count FROM dbo.Table1 GROUP BY Mark ) AS T2
)
SELECT Mark, Count, LEFT(Names, LEN(NAMES) - 1) AS Names
FROM DelimitedNames ;