Explication détaillée de la façon de modifier par lots la structure d'une table en PHP

<?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 &#39;pre_tb_%&#39;";
  $ret = mysql_query($sql);
  while($row = mysql_fetch_assoc($ret)){
   $info1[] = $row;
  }
  foreach ($info1 as $v) {
   $chidarr1[] = substr($v[&#39;Tables_in_multiopen (pre_tb_%)&#39;],7);//获取标记号
  }
  foreach ($chidarr1 as $val) {
   $tabname = &#39;stat_adclick_&#39;.$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);
?>