sql查询树形结构

A. sql server怎么对树形结构表的节点进行拼接

DECLARE @temp nvarchar(MAX)='',@pid bigint=3;
WHILE @pid<>0 BEGIN IF @temp=''
SELECT @temp=TypeName,@pid=ParentId
FROM [dbo].[Test]
WHERE Id=@pid;
ELSE
SELECT @temp=(TypeName+'->'+@temp),@pid=ParentId
FROM [dbo].[Test]
WHERE Id=@pid;
END;
SELECT @temp AS TypeName;