bbs树形结构的实现方法（一）

    bbs的树形结构显示可以有很多种方法，其中比较容易想到的是递归和排序串方法，但这两种方法并不是很好，那么怎样才算是比较合理的算法呢？
    递归方法不用讲，大家都知道怎么用，先讲讲排序串方法，最简单的排序串方法可以这样用,只用一个id就可以完成树型，向这样
1  001
2  002
3  001001
4  001001001
5  001002001
用这个字符串排序后就变成这样：
001
   001001
         001001001
   001002001
002
这种方法容易实现，但缺点也是很明显，一个是回帖数受限制，另一个随着回帖增加会越来越长，影响数据库效率。  

下面一种方法是李龙的，属于变通的排序串方法
DDL
--------------
CREATE TABLE dbo.Message
(
    ID          numeric(18,0) IDENTITY(1000,1),
    DateAndTime datetime      DEFAULT getdate() NOT NULL,
    AuthorID    numeric(18,0) NOT NULL,
    Subject     nvarchar(250) NOT NULL,
    Body        ntext         NULL,
    LinkURL     nvarchar(100) NULL,
    TextForLink nvarchar(50)  NULL,
    ImageURL    nvarchar(100) NULL,
    Class       int           DEFAULT 0 NOT NULL,
    ClientInfo  nvarchar(250) NULL,
    RemoteAddr  nvarchar(50)  NULL,
    CONSTRAINT PK_BBSMessage
    PRIMARY KEY NONCLUSTERED (ID,AuthorID)
)
go
CREATE TABLE dbo.MsgRefTab
(
    MsgID      numeric(18,0) NOT NULL,
    ParentID   numeric(18,0) NOT NULL,
    AncestorID numeric(18,0) NOT NULL,
    ChildNum   numeric(18,0) DEFAULT 0 NOT NULL,
    LinkStr    nvarchar(250) NOT NULL,
    CONSTRAINT PK_BBSRefTab
    PRIMARY KEY NONCLUSTERED (MsgID)
)
go
-----------------
存储过程:
-----------------
-- 抽出
CREATE PROCEDURE sp_Summary
@HaveBody bit,
@from numeric,
@to numeric
AS
IF (@HaveBody = 1)
select t.ID,t.DateAndTime,m.Nickname as
Author,m.Email,t.Subject,t.Body,t.LinkURL,t.TextForLink,t.ImageURL,s.ChildNu
m,s.ParentID
from Message t
  ,MsgRefTab AS s
  ,(SELECT MsgID FROM MsgRefTab WHERE ParentID = 0) AS f
  ,Members AS m
where t.ID=s.MsgID
  and f.MsgID = s.AncestorID
  and f.MsgID between @from and @to
  and m.MemberID = t.AuthorID
order by s.AncestorID,s.LinkStr
ELSE
select t.ID,t.DateAndTime,m.Nickname as
Author,m.Email,t.Subject,t.LinkURL,t.TextForLink,t.ImageURL,s.ChildNum,s.Par
entID
from Message t
  ,MsgRefTab AS s
  ,(SELECT MsgID FROM MsgRefTab WHERE ParentID = 0) AS f
  ,Members AS m
where t.ID=s.MsgID
  and f.MsgID = s.AncestorID
  and f.MsgID between @from and @to
  and m.MemberID = t.AuthorID
order by s.AncestorID,s.LinkStr
go

-- 加贴

CREATE PROCEDURE sp_Add_Message
@AuthorID numeric,
@Subject nvarchar(250),
@Body  ntext,
@LinkURL nvarchar(100),
@TextForLink nvarchar(50),
@ImageURL nvarchar(100),
@ParentID numeric,
@ID  numeric OUTPUT,
@ChildNum numeric OUTPUT,
@LinkStr nvarchar(250) OUTPUT,
@AncestorID numeric OUTPUT
AS
INSERT INTO Message(
  AuthorID,
  Subject,
  Body,
  LinkURL,
  TextForLink,
  ImageURL)
VALUES(
  @AuthorID,
  @Subject,
  @Body,
  @LinkURL,
  @TextForLink,
  @ImageURL)

SELECT @ID = @@IDENTITY

UPDATE MsgRefTab
SET
  ChildNum = ChildNum+1
WHERE
  MsgID = @ParentID

SELECT @ChildNum = ChildNum,
  @LinkStr = LinkStr,
  @AncestorID =