Please try:

SELECT
    Column1,
    STUFF(
    (SELECT ',' + Column2
       FROM YourTable t2
        WHERE t2.Column1=t1.Column1
        FOR XML PATH(''),type).value('.','nvarchar(max)'), 1, 1, '') AS Column2
FROM
    YourTable t1
GROUP BY Column1

Check LINK for more details.

Please try:

SELECT
    Column1,
    STUFF(
    (SELECT ',' + Column2
       FROM YourTable t2
        WHERE t2.Column1=t1.Column1
        FOR XML PATH(''),type).value('.','nvarchar(max)'), 1, 1, '') AS Column2
FROM
    YourTable t1
GROUP BY Column1

Check LINK for more details.

Please try:

SELECT
    Column1,
    STUFF(
    (SELECT ',' + Column2
       FROM YourTable
        FOR XML PATH(''),type).value('.','nvarchar(max)'), 1, 1, '') AS Column2
FROM
    YourTable
GROUP BY Column1

Check LINK for more details.

Please try:

SELECT
    Column1,
    STUFF(
    (SELECT ',' + Column2
       FROM YourTable t2
        WHERE t2.Column1=t1.Column1
        FOR XML PATH(''),type).value('.','nvarchar(max)'), 1, 1, '') AS Column2
FROM
    YourTable t1
GROUP BY Column1

Check LINK for more details.