示例表 tb 数据如下
id value
—————
1 aa
1 bb
2 aaa
2 bbb
2 ccc
第一种
SELECT
id,
[ val ] = ( SELECT [ value ] + ' , '
FROM tb AS b
WHERE b.id = a.id
FOR XML PATH( '' ) )
FROM tb AS a
[ val ] = ( SELECT [ value ] + ' , '
FROM tb AS b
WHERE b.id = a.id
FOR XML PATH( '' ) )
FROM tb AS a
1 aa,bb,
1 aa,bb,
2 aaa,bbb,ccc,
2 aaa,bbb,ccc,
2 aaa,bbb,ccc,
第二种
SELECT
id,
[ val ] = ( SELECT [ value ] + ' , '
FROM tb AS b
WHERE b.id = a.id
FOR XML PATH( '' ) )
FROM tb AS a
GROUP BY id
[ val ] = ( SELECT [ value ] + ' , '
FROM tb AS b
WHERE b.id = a.id
FOR XML PATH( '' ) )
FROM tb AS a
GROUP BY id
1 aa,bb,
2 aaa,bbb,ccc,
第三种 （用STUFF函数替换掉首端的逗号）
SELECT
id,
[ val ] = STUFF ( ( SELECT ' , ' + [ value ]
FROM tb AS b
WHERE b.id = a.id
FOR XML PATH( '' )) , 1 , 1 , '' )
FROM tb AS a
GROUP BY id
[ val ] = STUFF ( ( SELECT ' , ' + [ value ]
FROM tb AS b
WHERE b.id = a.id
FOR XML PATH( '' )) , 1 , 1 , '' )
FROM tb AS a
GROUP BY id
1 aa,bb
2 aaa,bbb,ccc
STUFF 函数将字符串插入另一字符串。它在第一个字符串中从开始位置删除指定长度的字符；然后将第二个字符串插入第一个字符串的开始位置。
STUFF ( character_expression , start , length ,character_expression_insert )
第四种 （用REPLACE函数将所有空格替换成逗号）
SELECT
id,
[ val ] = REPLACE ( ( SELECT [ value ] AS [ data() ]
FROM tb AS b
WHERE b.id = a.id
FOR XML PATH( '' )) , ' ' , ' , ' )
FROM tb AS a
GROUP BY id
[ val ] = REPLACE ( ( SELECT [ value ] AS [ data() ]
FROM tb AS b
WHERE b.id = a.id
FOR XML PATH( '' )) , ' ' , ' , ' )
FROM tb AS a
GROUP BY id
解析：[data()] 这里据说是起到一个类似数组的作用，具体用法还要再查。
如果外围不用REPLACE函数包住，则返回的结果是 aaa bbb ccc ，每项之间有空格，所以最后用REPLACE函数将所有空格替换成逗号
转自： http://www.cnblogs.com/aolin/archive/2011/04/12/2014122.html