下面的PHP程序将在数据库中搜索学生编号，如果找到，则显示详细信息，如果不存在，则显示消息。
<html>
<body>
<?php
$sno=$_POST['studNo'];
$connection = mysql_connect("localhost", "root", "")
or die("couldn't connect to the server");
$db = mysql_select_db("student", $connection)
or die("<b>connection fails");
$query = "select * from performance where Number = '$sno'";
if($result = mysql_query($query))
{
echo "<table border = 1 align = center>";
echo "<tr>";
echo "<th>Number<th>Name<th>Address<th>Mobile Number";
echo "</tr>";
while($row = mysql_fetch_array($result))
{
echo "<tr>";
echo "<th>",$row['Number'],"</th>";
echo "<th>",$row['Name'],"</th>";
echo "<th>",$row['Address'],"</th>";
echo "<th>",$row['MobileNo'],"</th>";
echo "</tr>";
}
echo "</table>";
echo "The student data updated";
}
else
{
echo "<b>Customer number does not exist";
}
mysql_close($connection);
?>
</body>
</html>
如果我搜索一个不存在的数字，则运行else块。当我给出一个存在的数字时，if块会运行，而while循环不会运行。有人能帮我吗？数据库字段名称正确。
mysql_query()仅在查询中出现错误时返回false。找不到任何匹配的行不是错误。要判断是否找到任何行，请使用mysql_num_rows()。
$result = mysql_query($query) or die("Query error: " . mysql_error());
if (mysql_num_rows($result) > 0) {
...
} else {
echo "<b>Customer number does not exist</b>";
}