Where子句中的未知列mysql查询

我的查询是$query = "SELECT * FROM cartmatch WHERE CARTNO=$cart4";，我收到一个错误，上面写着"where子句中的未知列'M833'"。正如你所知，cart4=M833。

：：编辑：：出于某种原因，什么都没有显示出来。这是页面上的代码。

<?php
$cart1 = rawurldecode($_GET["path"]);
list( , , , , , $cart2) = explode ("''", $cart1);
$cart3 = $cart2;
list($cart4) = explode (" ", $cart3);
$con = mysql_connect("SERVER","USERNAME","PASSWORD");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }
mysql_select_db("cartmatch", $con);
$result = mysql_query("SELECT * FROM cartmatch WHERE CARTNO='$cart4'");
while($row = mysql_fetch_array($result))
  {
echo '<form enctype="multipart/form-data" action="album.php" method="POST">Please enter press save.<br><br><input name="ID" type="hidden" value=';
echo $_GET["ID"];
echo ' ><input name="enabled" type="hidden" value=';
echo $_GET["enabled"];
echo ' ><input name="artist" type="hidden" value=';
echo $_GET["artist"];
echo ' ><input name="title" type="hidden" value="';
echo $_GET["title"];
echo '" >Name:<br/><input name="album" type="text" autofocus="autofocus" value="';
echo $row['ALBUM'];
echo '" ><input type="submit" name="edit" value="Save"></form>';
  }
mysql_close($con);
?>