php批量修改表结构

<?php
set_time_limit(0);
$con = mysql_connect("localhost", "root", "root");
$dbname = "db";
if ($con) {
  if (mysql_select_db($dbname, $con)) {
    $sql = "show tables like 'pre_tb_%'";
    $ret = mysql_query($sql);
    while($row = mysql_fetch_assoc($ret)){
      $info1[] = $row;
    }
    foreach ($info1 as $v) {
      $chidarr1[] = substr($v['Tables_in_multiopen (pre_tb_%)'],7);//获取标记号
    }
    foreach ($chidarr1 as $val) {
      $tabname = 'stat_adclick_'.$val;
      $sql = "alter table $tabname add column c2 int default 0 after p";
      mysql_query($sql);
      $sql = "alter table $tabname DROP PRIMARY KEY";
      mysql_query($sql);
      $sql = "alter table $tabname add primary key(c2,p)";
      mysql_query($sql);
      $sql = "alter table $tabname drop index old_index";
      mysql_query($sql);
      $sql = "create index idx_newincex on $tabname (c2,p)";
      mysql_query($sql);
    }
  }
}
mysql_close($con);
?>