Concatenate all the rows values into single row :

Script to create a table and load the data :
CREATE TABLE test_rowconcatenate
  (
     id   INT IDENTITY(1, 1),
     name VARCHAR(10)
  )

SELECT *
FROM   test_rowconcatenate

INSERT INTO test_rowconcatenate
VALUES     ('A'),
            ('B'),
            ('C'),
            ('D'),
            ('E'),
            ('F'),
            ('G'),
            ('H'),
            ('I'),
            ('J'),
            ('K'),
            ('L'),
            ('M'),
            ('N'),
            ('O'),
            ('P')

SELECT *
FROM   test_rowconcatenate

Ways to concatenate all the row values into single record :

1).

DECLARE @string VARCHAR(max) = ''

SELECT @string = @string + ',' + name
FROM   test_rowconcatenate

PRINT Substring(@string, 2, Len(@string))

2).
DECLARE @string VARCHAR(max)='',
        @field  VARCHAR(10)='',
        @i      INT = 1,
        @n      INT

SELECT @n = Count(0)
FROM   test_rowconcatenate

WHILE( @i <= @n )
  BEGIN
      SELECT @field = name
      FROM   (SELECT name,
                     Row_number()
                       OVER(
                         ORDER BY id) row_id
              FROM   test_rowconcatenate) a
      WHERE  row_id = @i

      SET @string = @string + ',' + @field
      SET @i = @i + 1
  END

PRINT Substring(@string, 2, Len(@string))

3).
DECLARE @string VARCHAR(max) ='',
        @field  VARCHAR(10)
DECLARE test_cur CURSOR FOR
  SELECT name
  FROM   test_rowconcatenate

OPEN test_cur

FETCH FROM test_cur INTO @field

WHILE @@Fetch_status = 0
  BEGIN
      SET @string = @string + ',' + @field

      FETCH FROM test_cur INTO @field
  END

CLOSE test_cur

DEALLOCATE test_cur

PRINT Stuff(@string, 1, 1, '')

4).
SELECT Stuff((SELECT ',' + name
              FROM   test_rowconcatenate
              FOR xml path('')), 1, 1, '')