sql FOR XML PATH('')

alter function test()
Returns nvarchar(max)
As
Begin
Declare @avg nvarchar(max)
Declare @str nvarchar(max)
Set @str=(
Select ','+yuanshidanhao from Aj_Jibenxinxi Where convert(nvarchar(max),id) in (1,2,6) FOR XML PATH('')
)
Return @str
End