Sample SQL script of a STUFF. In this example, there is a Deadlines table and if a date has more than one deadline, we want a single row per date and all deadlines to be in a comma-separated list.

SqlStuffManyValuesIntoRow.sql

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

-- =============================================
-- Description:	Returns table with deadlines. 
-- If there's more than one deadline on a date, all are added to a single row and are comma separated
-- =============================================
CREATE FUNCTION [dbo].[Deadlines]
(
 
)
RETURNS TABLE
AS
RETURN
(
	SELECT DISTINCT dd.DeadlineDate
	, STUFF((
        SELECT ', ' + dd2.DeadlineDescription
        FROM [dbo].[DeadlineDay] dd2
        WHERE dd2.DeadlineDate = dd.DeadlineDate
        ORDER BY dd2.DeadlineDate
        FOR XML PATH('')), 1, 2, ''
    ) AS Deadline
	FROM [dbo].[DeadlineDay] dd
);
GO