php如何向数据库中的某串数据后追加内容【急】

<code>$sql = "UPDATE tag SET  tag =concat(tag,'$biaoqian') WHERE id = '$xuehao'";
</code>

<code>学号:
<?php echo $_POST["xuehao"]; ?>
<?php echo "<br>"; ?>
tag:<?php echo $_POST["biaoqian"]; ?>
<?php echo "<br>"; ?>


<?php $mysql = new SaeMysql();

$sql = "SELECT * FROM `tag` LIMIT 10";
$data = $mysql->getData( $sql );



$biaoqian = $_POST['biaoqian'];
$xuehao = $_POST['xuehao'];

$sql = "UPDATE tag SET  tag =concat(tag,'$biaoqian') WHERE id = '$xuehao'";


$mysql->runSql($sql);
if ($mysql->errno() != 0)
{
    die("Error:" . $mysql->errmsg());
}

$mysql->closeDb();

echo $mysql->errmsg();   
</code>

<code>$sql = "UPDATE tag SET  tag =concat(tag,'$biaoqian') WHERE id = '$xuehao'";
</code>

<code>学号:
<?php echo $_POST["xuehao"]; ?>
<?php echo "<br>"; ?>
tag:<?php echo $_POST["biaoqian"]; ?>
<?php echo "<br>"; ?>


<?php $mysql = new SaeMysql();

$sql = "SELECT * FROM `tag` LIMIT 10";
$data = $mysql->getData( $sql );



$biaoqian = $_POST['biaoqian'];
$xuehao = $_POST['xuehao'];

$sql = "UPDATE tag SET  tag =concat(tag,'$biaoqian') WHERE id = '$xuehao'";


$mysql->runSql($sql);
if ($mysql->errno() != 0)
{
    die("Error:" . $mysql->errmsg());
}

$mysql->closeDb();

echo $mysql->errmsg();   
</code>