出现错误数据库未选择

code:

<?php
session_start();
$_SESSION['msg'] = "";
$con = mysql_connect('localhost','me','omglol');
mysql_select_db('test',$con);
$q = mysql_query(sprintf("select * from UserTable where (nick=\"%s\") AND (pass=SHA1(\"%s\"))",$_POST['nick'],$_POST['pass']),$con) or die(mysql_error());

这对我来说看起来很正确。是的，我知道“测试”的存在。并包含UserTable。

首先，感谢 Rid 将 php4 添加到我忘记的标签中:(

根据 Laser_wizard 的建议，我执行了以下操作：（整个代码）：

<?php
session_start();
$_SESSION['msg'] = "";
$con = mysql_connect('localhost','me','omglol');
if(!$con)
{
    die("The connection to mysql server is not being made.");
}
$db = 'test';
$selected = mysql_select_db($db,$con);
if(!$selected)
{
    die(sprintf("Cannot use database %s.",$db));
}
//$q = mysql_query(sprintf("select * from UserTable where (nick=\"%s\") AND (pass=SHA1(\"%s\"))",$_POST['nick'],$_POST['pass']),$con) or die(mysql_error());
$q = mysql_query("select * from UserTable",$con) or die("The query statement still isn't working");
$row = mysql_fetch_assoc($q);
$dest=0;
if(mysql_num_rows($q)==0)
{
    //$testn = mysql_query(sprintf("select * from UserTable where nick=(\"%s\")",$_POST['nick']),$con);
        $testn = mysql_query("select * from Category",$con) or die("The 2nd query statement still isn't working");
        if(mysql_num_rows($testn)==0)
        {
               $_SESSION['msg'] = "Nick ".$_POST['nick']." was not found. Check spelling or <a href=\\\"register.php\\\">register</a>";
        }
        else
        {
                $_SESSION['msg'] = "Password incorrect";
        }
        if(isset($_SESSION['attempts']))
        {
                $_SESSION['attempts'] = $_SESSION['attempts'] + 1;
        }
        else
        {
                $_SESSION['attempts'] = 1;
        }
    mysql_free_result($q);
    mysql_free_result($testn);
        mysql_close($con);
    $dest = 'Location:http://cs4.sunyocc.edu/~me/onestopshop/login.php';
}
else
{
        $_SESSION['nick'] = $_POST['nick'];
    $_SESSION['email'] = $row['email'];
    mysql_free_result($q);
    mysql_close($con);
    $dest = 'Location:http://cs4.sunyocc.edu/~me/onestopshop/index.php';
}
header($dest);
exit();
?>

与上面相同的错误。所以 $con 被设置并且 $selected 读取 true，所以我很困惑接下来要检查什么。我猜 mysql_select_db($db,$con); $testn 也不是仍然无法工作但仍然读取 true 吗？我很困惑下一步该做什么。

添加一些 die 语句来测试连接并确保其正在设置。 除此之外，我想说注释掉您的查询行，看看这是否会导致问题。

$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {
    die('Not connected : ' . mysql_error());
}

// make foo the current db
$db_selected = mysql_select_db('foo', $link);
if (!$db_selected) {
    die ('Can\'t use foo : ' . mysql_error());
}