[sql-server] Comma separated results in SQL

I have the following code which will create a comma delimited list for my results:

DECLARE @listStr VARCHAR(MAX)
SELECT @listStr = COALESCE(@listStr+', ' ,'') + INSTITUTIONNAME
FROM EDUCATION
WHERE STUDENTNUMBER= '111'
SELECT @listStr

The problem is its creating one massive comma delimited line. I need it to return a comma separated list per row.

So if Simon has been part of 2 institutions, then i expect:

"INSTITUTION1, INSTITUTION2"

As i didnt supply a where clause i expect my results to show up like this for each row in the database.

If you're stuck with SQL Server <2017, you can use GroupConcat. The syntax and the performance is far better than the FOR XML PATH sollution.

Installation:

-- https://codeplexarchive.blob.core.windows.net/archive/projects/groupconcat/groupconcat.zip
create assembly [GroupConcat] from 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with permission_set = safe;
create aggregate [dbo].[GROUP_CONCAT]    (@VALUE [nvarchar](4000))                                                      returns[nvarchar](max) external name [GroupConcat].[GroupConcat.GROUP_CONCAT];
create aggregate [dbo].[GROUP_CONCAT_D]  (@VALUE [nvarchar](4000), @DELIMITER [nvarchar](4))                            returns[nvarchar](max) external name [GroupConcat].[GroupConcat.GROUP_CONCAT_D];
create aggregate [dbo].[GROUP_CONCAT_DS] (@VALUE [nvarchar](4000), @DELIMITER [nvarchar](4), @SORT_ORDER [tinyint])     returns[nvarchar](max) external name [GroupConcat].[GroupConcat.GROUP_CONCAT_DS];
create aggregate [dbo].[GROUP_CONCAT_S]  (@VALUE [nvarchar](4000), @SORT_ORDER [tinyint])                               returns[nvarchar](max) external name [GroupConcat].[GroupConcat.GROUP_CONCAT_S];

go

Usage:

declare @liststr varchar(max)
select @liststr = dbo.group_concat_d(institutionname, ',')
from education
where studentnumber = '111'
group by studentnumber;
select @liststr

GroupConcat does not support ordering, though. You could use PIVOT, CTE's and windows functions if you need ordering:

drop table if exists #students;
create table #students (
    name        varchar(20),
    institution varchar(20),
    year        int -- order by year
)
go

insert into #students(name, institution, year)
values
    ('Simon', 'INSTITUTION1', 2005),
    ('Simon', 'INSTITUTION2', 2008);

with cte as (
    select name,
           institution,
           rn = row_number() over (partition by name order by year)
    from #students
)
select name,
       [1] +
       isnull((',' + [2]), '') +
       isnull((',' + [3]), '') +
       isnull((',' + [4]), '') +
       isnull((',' + [5]), '') +
       isnull((',' + [6]), '') +
       isnull((',' + [7]), '') +
       isnull((',' + [8]), '') +
       isnull((',' + [9]), '') +
       isnull((',' + [10]), '') +
       isnull((',' + [11]), '') +
       isnull((',' + [12]), '') +
       isnull((',' + [13]), '') +
       isnull((',' + [14]), '') +
       isnull((',' + [15]), '') +
       isnull((',' + [16]), '') +
       isnull((',' + [17]), '') +
       isnull((',' + [18]), '') +
       isnull((',' + [19]), '') +
       isnull((',' + [20]), '')
from cte
    pivot (
    max(institution)
    for rn in ([1], [2], [3], [4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20])
    ) as piv

I just saw another question very similar to this!

Here is the canonical NORTHWIND (spelled just slightly different for some reason) database example.

SELECT *
FROM [NORTHWND].[dbo].[Products]

SELECT CategoryId,
           MAX( CASE seq WHEN 1 THEN ProductName ELSE '' END ) + ', ' +
           MAX( CASE seq WHEN 2 THEN ProductName ELSE '' END ) + ', ' +
           MAX( CASE seq WHEN 3 THEN ProductName ELSE '' END ) + ', ' +
           MAX( CASE seq WHEN 4 THEN ProductName ELSE '' END )
      FROM ( SELECT p1.CategoryId, p1.ProductName,
                    ( SELECT COUNT(*) 
                        FROM NORTHWND.dbo.Products p2
                        WHERE p2.CategoryId = p1.CategoryId
                        AND p2.ProductName <= p1.ProductName )
             FROM NORTHWND.dbo.Products p1 ) D ( CategoryId, ProductName, seq )
     GROUP BY CategoryId ;

For Sql Server 2017 and later you can use the new STRING_AGG function

https://docs.microsoft.com/en-us/sql/t-sql/functions/string-agg-transact-sql

The following example replaces null values with 'N/A' and returns the names separated by commas in a single result cell.

SELECT STRING_AGG ( ISNULL(FirstName,'N/A'), ',') AS csv 
FROM Person.Person;

Here is the result set.

John,N/A,Mike,Peter,N/A,N/A,Alice,Bob

Perhaps a more common use case is to group together and then aggregate, just like you would with SUM, COUNT or AVG.

SELECT a.articleId, title, STRING_AGG (tag, ',') AS tags 
FROM dbo.Article AS a       
LEFT JOIN dbo.ArticleTag AS t 
    ON a.ArticleId = t.ArticleId 
GROUP BY a.articleId, title;

this works in sql server 2016

USE AdventureWorks
GO
DECLARE @listStr VARCHAR(MAX)
SELECT @listStr = COALESCE(@listStr+',' ,'') + Name
FROM Production.Product
SELECT @listStr
GO