How to coalesce many rows into one? - sql-server

Question

I am using SSMS 2008 R2 and am simply trying to coalesce many rows into one. This should be simple I think, but it is currently repeating data in each row. Consider:
create table test
(
Name varchar(30)
)
insert test values('A'),('B'),('C')
select * from test
select distinct Name, coalesce(Name + ', ', '')
from test
How can I rewrite this to achieve one row like:
A,B,C

Answer 1

SELECT STUFF(( SELECT ', ' + Name
from #test
FOR XML PATH(''), TYPE).
value('.','NVARCHAR(MAX)'),1,2,'')
RESULT: A, B, C
I am sure this not how exactly your rows look that you are trying to concatenate, therefore see below for a slightly different data set and how you would go about doing this kind of operation on that
Test Data
create table #test
(
Id INT,
Name varchar(30)
)
insert #test values
(1,'A'),(1,'B'),(1,'C'),(2,'E'),(2,'F'),(2,'G')
Query
select t.Id
, STUFF(( SELECT ', ' + Name
from #test
WHERE Id = T.Id
FOR XML PATH(''), TYPE).
value('.','NVARCHAR(MAX)'),1,2,'') AS List
FROM #test t
GROUP BY t.Id
Result Set
╔════╦═════════╗
║ Id ║ List ║
╠════╬═════════╣
║ 1 ║ A, B, C ║
║ 2 ║ E, F, G ║
╚════╩═════════╝

Answer 2

In SQL Server Transact-SQL, the easiest way to accomplish this is the following.
A table like this:
create table #foo
(
id int not null identity(1,1) primary key clustered ,
name varchar(32) not null ,
)
insert #foo (name) values ( 'a' )
insert #foo (name) values ( 'b' )
insert #foo (name) values ( 'c' )
insert #foo (name) values ( 'd' )
go
Can flattened using this seemingly dubious (but documented) technique:
declare #text varchar(max) = ''
select #text = #text
+ case len(#text)
when 0 then ''
else ','
end
+ t.name
from #foo t
select list_of_names = #text
go
yielding
list_of_names
-------------
a,b,c,d
Easy!

Answer 3

in the old days of SQL Server 7.0 and SQL Server 2000, I Used to do this with a variable and using COALESCE like this:
DECLARE #List VARCHAR(8000)
SELECT #List = COALESCE(#List + ',', '') + CAST(Color AS VARCHAR)
FROM NameColorTable
SELECT #List
But after SQL Server 2005 and XPATH appearance, this the way I prefer to use:
SELECT STUFF((
select ','+ cast(Color as nvarchar(255))
from NameColorTable b
WHERE a.Name = b.Name
FOR XML PATH('')
)
,1,1,'') AS COLUMN2
FROM NameColorTable a
GROUP BY a.Name
I have a blog post about this here:
https://koukia.ca/stuff-vs-coalesce-in-tsql-for-concatenating-row-values-aefb078536f8#.f4iggl22y

Answer 4

Here is the standard solution for concatenation using XML PATH()
SELECT
STUFF(
(
SELECT
',' + Name
FROM test
FOR XML PATH(''),TYPE
).value('.','VARCHAR(MAX)'
), 1, 1, ''
) As list
Another option can be using the new SQL CONCAT() function introduced with SQL Server 2012.
I used SQL Concat() in the below sample
declare #namelist nvarchar(max)
select #namelist = concat(isnull(#namelist+',',''), name) from test2
select #namelist