DECLARE @SQL AS VARCHAR(8000)
SELECT @SQL = ISNULL(@SQL+',','') + ColumnName FROM TableName
SELECT @SQL
STRING_AGG: Applies to SQL Server 2017 (14.x) and later
DECLARE @Table2 TABLE(ID INT, Value INT);
INSERT INTO @Table1 VALUES (1,100),(1,200),(1,300),(1,400);
SELECT ID , STRING_AGG([Value], ', ') AS List_Output
FROM @Table2
GROUP BY ID;
-- OR
DECLARE @Table1 TABLE(ID INT, Value INT)
INSERT INTO @Table1 VALUES (1,100),(1,200),(1,300),(1,400)
SELECT ID
,STUFF((SELECT ', ' + CAST(Value AS VARCHAR(10)) [text()]
FROM @Table1
WHERE ID = t.ID
FOR XML PATH(''), TYPE)
.value('.','NVARCHAR(MAX)'),1,1,' ') List_Output
FROM @Table1 t
GROUP BY ID