常用递归结构数据表,返会指点节点,跟其子节点的操作

内容来自机械工业出版的仓库管理系统设计一书
表结构{WareHouserID , ParentWarehouseID }
查询指定节点跟其子节点的信息
ALTER  FUNCTION dbo.GetWareSubtreeInfo(@WareHouseID int)
RETURNS @treeinfo table
(
[WareHouseID] [int] NOT NULL,
[ParentWarehouseID] [int] NOT NULL,
[Level] [int] NOT NULL
) AS
BEGIN
 --返回所有仓库，不按层次
 IF @WareHouseID=0
 BEGIN
  INSERT INTO @treeinfo
  SELECT WareHouseID,0,0  From  [WareHouses]
  RETURN
 END
 
 DECLARE @level AS int
 SELECT @level = 0
 
 INSERT INTO @treeinfo
 SELECT WareHouseID, ParentWarehouseID, @level
 From [WareHouses]
 WHERE [WareHouseID] = @WareHouseID

----每次循环是@level会加1,这样做Join 连接时会不断的将子类,以及子来的子类逐步添加到临时表 里
 WHILE @@ROWCOUNT > 0
 BEGIN
 
  SET @level = @level + 1
  
  INSERT INTO @treeinfo
  
  SELECT D.WareHouseID, D.ParentWarehouseID, @level
  From [WareHouses] As D
  JOIN @treeinfo AS T
  ON D.[ParentWarehouseID] = T.[WareHouseID] AND T.[Level] = @level - 1
 
 END
 RETURN
END