實(shí)現(xiàn)樹(shù)狀結(jié)構(gòu)的兩種方法1。遞歸法
遞歸是指在函數(shù)中顯式的調(diào)用它自身。
利用遞歸法實(shí)現(xiàn)樹(shù)狀結(jié)構(gòu)的特點(diǎn)是寫(xiě)入數(shù)據(jù)速度較快，顯示速度較慢（在樹(shù)的分支/層次較多的情況下尤其明顯）。適用與寫(xiě)入數(shù)據(jù)量大，樹(shù)的結(jié)構(gòu)復(fù)雜的情況下。
數(shù)據(jù)結(jié)構(gòu)(以mysql為例)

代碼:--------------------------------------------------------------------------------
CREATE TABLE `tree1` (
  `id` tinyint(3) unsigned NOT NULL auto_increment,
  `parentid` tinyint(3) unsigned NOT NULL default '0',
  `topic` varchar(50) default NULL,
  PRIMARY KEY  (`id`),
  KEY `parentid` (`parentid`)
) TYPE=MyISAM;

INSERT INTO `tree1` (`id`, `parentid`, `topic`) VALUES
  (1,0,'樹(shù)1'),
  (2,0,'樹(shù)2'),
  (3,0,'樹(shù)3'),
  (4,2,'樹(shù)2-1'),
  (5,4,'樹(shù)2-1-1'),
  (6,2,'樹(shù)2-2'),
  (7,1,'樹(shù)1-1'),
  (8,1,'樹(shù)1-2'),
  (9,1,'樹(shù)1-3'),
  (10,8,'樹(shù)1-2-1'),
  (11,7,'樹(shù)1-1-1'),
  (12,11,'樹(shù)1-1-1-1');
--------------------------------------------------------------------------------


字段說(shuō)明
id,記錄的id號(hào)
parentid,記錄的父記錄id（為0則為根記錄）
topic,記錄的顯示標(biāo)題

顯示程序

順序樹(shù):

PHP代碼:--------------------------------------------------------------------------------

<?
/* 數(shù)據(jù)庫(kù)連接 */
mysql_connect();
mysql_select_db('tree');

/* 樹(shù)狀顯示的遞歸函數(shù) */
function tree($parentid = 0) {
    /*執(zhí)行sql查詢(xún)，獲取記錄的標(biāo)題和id*/
    $sql = "select topic,id from tree1 where parentid = $parentid order by id asc";
    $rs = mysql_query($sql);
    /* 縮進(jìn)*/
    echo("<ul>");
    while($ra = mysql_fetch_row($rs)) {
        /* 顯示記錄標(biāo)題 */
        echo('<li>'.$ra[0].'</li>');
        /* 遞歸調(diào)用 */
        tree($ra[1]);
    }
    echo("</ul>");
}
tree();
?>

--------------------------------------------------------------------------------


逆序樹(shù):

PHP代碼:--------------------------------------------------------------------------------

<?
/* 數(shù)據(jù)庫(kù)連接 */
mysql_connect();
mysql_select_db('tree');

/* 樹(shù)狀顯示的遞歸函數(shù) */
function tree($parentid = 0) {
    /*執(zhí)行sql查詢(xún)，獲取記錄的標(biāo)題和id*/
    $sql = "select topic,id from tree1 where parentid = $parentid order by id desc";
    $rs = mysql_query($sql);
    /* 縮進(jìn)*/
    echo("<ul>");
    while($ra = mysql_fetch_row($rs)) {
        /* 顯示記錄標(biāo)題 */
        echo('<li>'.$ra[0].'</li>');
        /* 遞歸調(diào)用 */
        tree($ra[1]);
    }
    echo("</ul>");
}
tree();
?>

--------------------------------------------------------------------------------


插入數(shù)據(jù)程序

PHP代碼:--------------------------------------------------------------------------------

<?
/* 數(shù)據(jù)庫(kù)連接 */
mysql_connect();
mysql_select_db('tree');
$sql = "insert into tree (topic,parentid) values('樹(shù)3-1',3);";
mysql_query($sql);
?>

--------------------------------------------------------------------------------


2。排序字段法
此方法是通過(guò)在數(shù)據(jù)結(jié)構(gòu)中增加一個(gè)標(biāo)志記錄在整個(gè)樹(shù)中的順序位置的字段來(lái)實(shí)現(xiàn)的。特點(diǎn)是顯示速度和效率高。但在單個(gè)樹(shù)的結(jié)構(gòu)復(fù)雜的情況下，數(shù)據(jù)寫(xiě)入效率有所不足。而且順序排列時(shí)候，插入，刪除記錄的算法過(guò)于復(fù)雜，故通常用逆序排列。

數(shù)據(jù)結(jié)構(gòu)(以mysql為例)

代碼:--------------------------------------------------------------------------------
CREATE TABLE `tree2` (
  `id` tinyint(3) unsigned NOT NULL auto_increment,
  `parentid` tinyint(3) unsigned NOT NULL default '0',
  `rootid` tinyint(3) unsigned NOT NULL default '0',
  `layer` tinyint(3) unsigned NOT NULL default '0',
  `orders` tinyint(3) unsigned NOT NULL default '0',
  `topic` varchar(50) default NULL,
  PRIMARY KEY  (`id`),
  KEY `parentid` (`parentid`),
  KEY `rootid` (`rootid`)
) TYPE=MyISAM

INSERT INTO `tree2` (`id`, `parentid`, `rootid`, `layer`, `orders`, `topic`) VALUES
  (1,0,1,0,0,'樹(shù)1'),
  (2,0,2,0,0,'樹(shù)2'),
  (3,0,3,0,0,'樹(shù)3'),
  (4,2,2,1,2,'樹(shù)2-1'),
  (5,4,2,2,3,'樹(shù)2-1-1'),
  (6,2,2,1,1,'樹(shù)2-2'),
  (7,1,1,1,4,'樹(shù)1-1'),
  (8,1,1,1,2,'樹(shù)1-2'),
  (9,1,1,1,1,'樹(shù)1-3'),
  (10,8,1,2,3,'樹(shù)1-2-1'),
  (11,7,1,2,5,'樹(shù)1-1-1'),
  (12,11,1,3,6,'樹(shù)1-1-1-1');
--------------------------------------------------------------------------------


顯示程序

PHP代碼:--------------------------------------------------------------------------------

<?
/* 數(shù)據(jù)庫(kù)連接 */
mysql_connect();
mysql_select_db('tree');

/* 選出所有根記錄id */
$sql = "select id from tree2 where parentid = 0 order by id desc";
$rs = mysql_query($sql);
echo("<ul>");
$lay = 0;
while($ra = mysql_fetch_row($rs)) {
    echo("<ul>");
    /* 選出此樹(shù)所有記錄，并按orders字段排序 */
    $sql = "select topic,layer from tree2 where rootid = $ra[0] order by orders";
    $rs1 = mysql_query($sql);
    while($ra1 = mysql_fetch_row($rs1)) {
        /* 縮進(jìn)顯示 */
        if($ra1[1]>$lay) {
            echo(str_repeat("<ul>",$ra1[1]-$lay));
        }elseif($ra1[1]<$lay) {
            echo(str_repeat("</ul>",$lay-$ra1[1]));
        }
        /* 記錄顯示 */
        //echo("$ra1[1]>$lay");
        echo("<li>$ra1[0]</li>");
        $lay = $ra1[1];
    }
    echo("</ul>");
}
echo("</ul>");
?>

--------------------------------------------------------------------------------


插入數(shù)據(jù)程序

PHP代碼:--------------------------------------------------------------------------------

<?
/* 數(shù)據(jù)庫(kù)連接 */
mysql_connect();
mysql_select_db('tree');

/* 插入根記錄 */
$sql = "insert into tree2 (topic) values ('樹(shù)5')";
mysql_query($sql);
$sql = "update tree2 set rootid = id where id = ".mysql_insert_id();
mysql_query($sql);

/* 插入子記錄 */
$parentid = 5;//父記錄id
/* 取出 根記錄id,父記錄縮進(jìn)層次,父記錄順序位置 */
$sql = "select rootid,layer,orders from tree2 where id = $parentid";
list($rootid,$layer,$orders) = mysql_fetch_row(mysql_query($sql));
/* 更新插入位置后記錄的orders值 */
$sql = "update tree2 set orders = orders + 1 where orders > $orders";
mysql_query($sql);
/* 插入記錄 */
$sql = "insert into tree2 (rootid,parentid,orders,layer,topic) values ($rootid,$parentid,".($orders+1).",".($layer+1).",'樹(shù)2-1-1-2')";
mysql_query($sql);?>