PHP操作数据库 动态创建字段

PHP操作数据库时自动创建字段，如下代码：

html> 
head> 
meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> 
title>动态创建字段 - www.cxybl.comtitle> 
style type="text/css"> 
 
style> 
head> 
 
body> 
form id="form1" name="form1" method="post" action="index_ok.php"> 
  table width="467" height="289" border="0" cellpadding="0" cellspacing="0"> 
    tr> 
      td width="168" height="89"> td> 
      td width="289"> td> 
    tr> 
    tr> 
      td height="30" align="right">span class="STYLE1">选择表 span>td> 
      td class="STYLE1">input name="table" type="text" id="table" size="20" />td> 
    tr> 
    tr> 
      td height="30" align="right">span class="STYLE1">字段 span>td> 
      td class="STYLE1">input name="field" type="text" id="field" size="20">td> 
    tr> 
    tr> 
      td height="30" align="right">span class="STYLE1">类型 span>td> 
      td class="STYLE1">select name="type" id="type"> 
        option>intoption> 
        option>textoption> 
        option>dateoption> 
        option>doubleoption> 
        option>varcharoption> 
        option>datetimeoption> 
        option>bloboption> 
      select>      td> 
    tr> 
    tr> 
      td height="30" align="right">span class="STYLE1">长度 span>td> 
      td class="STYLE1">input name="length" type="text" id="length" size="15">td> 
    tr> 
    tr> 
      td height="30" align="right">span class="STYLE1">NULL span>td> 
      td class="STYLE1">input type="radio" name="null" value="null"> 
        null 
        input type="radio" name="null" value="not null"> 
        not null td> 
    tr> 
    tr> 
      td height="30" align="right"> td> 
      td>input type="submit" name="Submit" value="提交" />td> 
    tr> 
    tr> 
      td height="20" align="right"> td> 
      td> td> 
    tr> 
  table> 
form> 
body> 
html> 

conn.php:

$id=mysql_connect("localhost","root","mysql") or die('连接失败:' . mysql_error()); 
if(mysql_select_db("phpjcdb",$id))  //说明：phpjcdb 是数据库名称 
  echo ""; 
  else 
  echo ('数据库选择失败:' . mysql_error()); 
mysql_query("set names gb2312");  //设置为简体中文 
?> 

index_ok.php:

session_start();  
include("conn.php"); 
if($_POST['Submit']==true){ 
  $null=$_POST[null]; 
  $table = $_POST['table']; 
  $field = $_POST['field']; 
  $type = $_POST['type']; 
  $length = $_POST['length']; 
  $mysql=mysql_query("alter table $table add $field $type($length) $null"); 
    echo mysql_error(); 
  if($mysql==true){ 
    echo "字段添加成功!"; 
  }else{echo "添加失败!";} 
} 
?>