sql server - T-SQL: Combine rows to one row

I have the following table:

number  word
======  ====
1       AAA
2       BBB
2       CCCC
4       CCCC

4       BBB
4       AAA

Now I want to create a new table, where a "number" only occurs in one row. The corresponding values in "word" should be converted to comma sepeareted string.

The result table:

number  word
======  ====

1       AAA
2       BBB,CCCC
4       CCCCC,BBB,AAA

How can this solved with T-SQL? Thanks in advance.

Answer

I started so I may as well post mine too...

CREATE TABLE #test

(
    ID tinyint
    ,Word varchar(20)
);
INSERT INTO #test
VALUES
(1,'aaa')
,(1,'bbb')
,(2,'abc')
,(2,'def')

,(2,'ghi')
,(3,'zzz');

SELECT DISTINCT
a.ID
,STUFF((
    SELECT
        ',' + b.Word
    FROM #test b
    WHERE a.ID = b.ID 

    FOR XML PATH('')
),1,1,'') AS [Contains]
FROM #test a