Peter
Paul
Mary

SubjectID       StudentName
----------      -------------
1               Mary
1               John
1               Sam
2               Alaina
2               Edward

SubjectID       StudentName
----------      -------------
1               Mary, John, Sam
2               Alaina, Edward

Select Main.SubjectID,
       Left(Main.Students,Len(Main.Students)-1) As "Students"
From
    (
        Select distinct ST2.SubjectID,
            (
                Select ST1.StudentName + ',' AS [text()]
                From dbo.Students ST1
                Where ST1.SubjectID = ST2.SubjectID
                ORDER BY ST1.SubjectID
                For XML PATH ('')
            ) [Students]
        From dbo.Students ST2
    ) [Main]

Select distinct ST2.SubjectID,
    substring(
        (
            Select ','+ST1.StudentName  AS [text()]
            From dbo.Students ST1
            Where ST1.SubjectID = ST2.SubjectID
            ORDER BY ST1.SubjectID
            For XML PATH ('')
        ), 2, 1000) [Students]
From dbo.Students ST2

SELECT FName + ', ' AS 'data()'
FROM NameList
FOR XML PATH('')

"Peter, Paul, Mary, "

STUFF(REPLACE((SELECT '#!' + LTRIM(RTRIM(FName)) AS 'data()' FROM NameList
FOR XML PATH('')),' #!',', '), 1, 2, '') as Brands

SELECT Stuff(
  (SELECT N', ' + Name FROM Names FOR XML PATH(''),TYPE)
  .value('text()[1]','nvarchar(max)'),1,2,N'')

SELECT per.ID,
Emails = JSON_VALUE(
   REPLACE(
     (SELECT _ = em.Email FROM Email em WHERE em.Person = per.ID FOR JSON PATH)
    ,'"},{"_":"',', '),'$[0]._'
)
FROM Person per

Id  Emails
1   abc@gmail.com
2   NULL
3   def@gmail.com, xyz@gmail.com

SELECT STRING_AGG(Name, ', ') AS Departments
FROM HumanResources.Department;

SELECT GroupName, STRING_AGG(Name, ', ') AS Departments
FROM HumanResources.Department
GROUP BY GroupName;

SELECT GroupName, STRING_AGG(Name, ', ') WITHIN GROUP (ORDER BY Name ASC) AS Departments
FROM HumanResources.Department
GROUP BY GroupName;

SELECT 1 AS a, GROUP_CONCAT(name ORDER BY name ASC SEPARATOR ', ') AS people
FROM users
WHERE id IN (1,2,3)
GROUP BY a

Declare @Numbers AS Nvarchar(MAX) -- It must not be MAX if you have few numbers
SELECT  @Numbers = COALESCE(@Numbers + ',', '') + Number
FROM   TableName where Number IS NOT NULL

SELECT @Numbers

102,103,104

postgres=# c test
You are now connected to database "test" as user "hgimenez".
test=# create table names (name text);
CREATE TABLE
test=# insert into names (name) values ('Peter'), ('Paul'), ('Mary');
INSERT 0 3
test=# select * from names;
 name
-------
 Peter
 Paul
 Mary
(3 rows)

test=# select array_agg(name) from names;
 array_agg
-------------------
 {Peter,Paul,Mary}
(1 row)

test=# select array_to_string(array_agg(name), ', ') from names;
 array_to_string
-------------------
 Peter, Paul, Mary
(1 row)

COLUMN employees FORMAT A50

SELECT deptno, LISTAGG(ename, ',') WITHIN GROUP (ORDER BY ename) AS employees
FROM   emp
GROUP BY deptno;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 ADAMS,FORD,JONES,SCOTT,SMITH
        30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD

3 rows selected.

DECLARE @t table
(
    Id int,
    Name varchar(10)
)
INSERT INTO @t
SELECT 1,'a' UNION ALL
SELECT 1,'b' UNION ALL
SELECT 2,'c' UNION ALL
SELECT 2,'d'

SELECT ID,
stuff(
(
    SELECT ','+ [Name] FROM @t WHERE Id = t.Id FOR XML PATH('')
),1,1,'')
FROM (SELECT DISTINCT ID FROM @t ) t

DECLARE @names VARCHAR(500)

SELECT @names = @names + ' ' + Name
FROM Names

select string_agg(name, ',')
from names;

;with basetable as
(   SELECT id, CAST(name as varchar(max))name,
        ROW_NUMBER() OVER(Partition By id     order by seq) rw,
        COUNT(*) OVER (Partition By id) recs
FROM (VALUES (1, 'Johnny', 1), (1,'M', 2),
                  (2,'Bill', 1), (2, 'S.', 4), (2, 'Preston', 5), (2, 'Esq.', 6),
        (3, 'Ted', 1), (3,'Theodore', 2), (3,'Logan', 3),
                  (4, 'Peter', 1), (4,'Paul', 2), (4,'Mary', 3)

           )g(id, name, seq)
),
rCTE as (
    SELECT recs, id, name, rw from basetable where rw=1
    UNION ALL
    SELECT b.recs, r.ID, r.name +', '+ b.name name, r.rw+1
    FROM basetable b
         inner join rCTE r
    on b.id = r.id and b.rw = r.rw+1
)
SELECT name FROM rCTE
WHERE recs = rw and ID=4

DECLARE @char VARCHAR(MAX);

SELECT @char = COALESCE(@char + ', ' + [column], [column])
FROM [table];

PRINT @char;

REPLACE(
        (select FName AS 'data()'  from NameList  for xml path(''))
         , ' ', ', ')

select substring(
        (select ', '+Name AS 'data()' from Names for xml path(''))
       ,3, 255) as "MyList"

DECLARE @Names VARCHAR(8000)
SELECT @name = ''
SELECT @Names = @Names + ',' + Names FROM People
SELECT SUBSTRING(2, @Names, 7998)

SELECT
    Table_Name
    ,STUFF((
        SELECT ',' + Column_Name
        FROM INFORMATION_SCHEMA.Columns Columns
        WHERE Tables.Table_Name = Columns.Table_Name
        ORDER BY Column_Name
        FOR XML PATH ('')), 1, 1, ''
    )Columns
FROM INFORMATION_SCHEMA.Columns Tables
GROUP BY TABLE_NAME

SELECT question_id,
   LISTAGG(element_id, ',') WITHIN GROUP (ORDER BY element_id)
FROM YOUR_TABLE;
GROUP BY question_id

DECLARE @names VARCHAR(500)
SELECT @names = CONCAT(@names, ' ', name)
FROM Names
select @names

CREATE Assembly concat_assembly
   AUTHORIZATION dbo
   FROM '<PATH TO Concat.dll IN SERVER>'
   WITH PERMISSION_SET = SAFE;
GO

CREATE AGGREGATE dbo.concat (

    @Value NVARCHAR(MAX)
  , @Delimiter NVARCHAR(4000)

) RETURNS NVARCHAR(MAX)
EXTERNAL Name concat_assembly.[Concat.Concat];
GO

sp_configure 'clr enabled', 1;
RECONFIGURE

SELECT dbo.Concat(field1, ',')
FROM Table1

___________________________
| id   |  rowList         |
|-------------------------|
| 0    | 6, 9             |
| 1    | 1,2,3,4,5,7,8,1  |
|_________________________|

CREATE TABLE `Data` (
  `id` int(11) NOT NULL,
  `user_id` int(11) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=latin1;


INSERT INTO `Data` (`id`, `user_id`) VALUES
(1, 1),
(2, 1),
(3, 1),
(4, 1),
(5, 1),
(6, 0),
(7, 1),
(8, 1),
(9, 0),
(10, 1);


CREATE TABLE `User` (
  `id` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;


INSERT INTO `User` (`id`) VALUES
(0),
(1);

SELECT User.id, GROUP_CONCAT(Data.id ORDER BY Data.id) AS rowList FROM User LEFT JOIN Data ON User.id = Data.user_id GROUP BY User.id

DECLARE @names VARCHAR(MAX)
SET @names = ''

SELECT @names = @names + ', ' + Name FROM Names

-- Deleting last two symbols (', ')
SET @sSql = LEFT(@sSql, LEN(@sSql) - 1)

with lines as
(
  select
    row_number() over(order by id) id, -- id is a line id
    line -- line of text.
  from
    source -- line source
),
result_lines as
(
  select
    id,
    cast(line as nvarchar(max)) line
  from
    lines
  where
    id = 1
  union all
  select
    l.id,
    cast(r.line + N', ' + l.line as nvarchar(max))
  from
    lines l
    inner join
    result_lines r
    on
      l.id = r.id + 1
)
select top 1
  line
from
  result_lines
order by
  id desc

create table #test (id int,name varchar(10))
--use separate inserts on older versions of SQL Server
insert into #test values (1,'Peter'), (1,'Paul'), (1,'Mary'), (2,'Alex'), (3,'Jack')

DECLARE @t VARCHAR(255)
SELECT @t = ISNULL(@t + ',' + name, name) FROM #test WHERE id = 1
select @t
drop table #test

Peter,Paul,Mary

DECLARE @Names VARCHAR(8000)
SELECT @Names = COALESCE(COALESCE(@Names + ', ', '') + Name, @Names) FROM People

CREATE TABLE dbo.Students
(
    StudentId INT
    , Name VARCHAR(50)
    , CONSTRAINT PK_Students PRIMARY KEY (StudentId)
);

CREATE TABLE dbo.Subjects
(
    SubjectId INT
    , Name VARCHAR(50)
    , CONSTRAINT PK_Subjects PRIMARY KEY (SubjectId)
);

CREATE TABLE dbo.Schedules
(
    StudentId INT
    , SubjectId INT
    , CONSTRAINT PK__Schedule PRIMARY KEY (StudentId, SubjectId)
    , CONSTRAINT FK_Schedule_Students FOREIGN KEY (StudentId) REFERENCES dbo.Students (StudentId)
    , CONSTRAINT FK_Schedule_Subjects FOREIGN KEY (SubjectId) REFERENCES dbo.Subjects (SubjectId)
);

INSERT dbo.Students (StudentId, Name) VALUES
    (1, 'Mary')
    , (2, 'John')
    , (3, 'Sam')
    , (4, 'Alaina')
    , (5, 'Edward')
;

INSERT dbo.Subjects (SubjectId, Name) VALUES
    (1, 'Physics')
    , (2, 'Geography')
    , (3, 'French')
    , (4, 'Gymnastics')
;

INSERT dbo.Schedules (StudentId, SubjectId) VALUES
    (1, 1)      --Mary, Physics
    , (2, 1)    --John, Physics
    , (3, 1)    --Sam, Physics
    , (4, 2)    --Alaina, Geography
    , (5, 2)    --Edward, Geography
;

SELECT
    sub.SubjectId
    , sub.Name AS [SubjectName]
    , ISNULL( x.Students, '') AS Students
FROM
    dbo.Subjects sub
    OUTER APPLY
    (
        SELECT
            CASE ROW_NUMBER() OVER (ORDER BY stu.Name) WHEN 1 THEN '' ELSE ', ' END
            + stu.Name
        FROM
            dbo.Students stu
            INNER JOIN dbo.Schedules sch
                ON stu.StudentId = sch.StudentId
        WHERE
            sch.SubjectId = sub.SubjectId
        ORDER BY
            stu.Name
        FOR XML PATH('')
    ) x (Students)
;

DECLARE @MyList VARCHAR(1000), @Delimiter CHAR(2) = ', '
SELECT @MyList = CASE WHEN @MyList > '' THEN @MyList + @Delimiter ELSE '' END + FieldToConcatenate FROM MyData