警告: mysqli_query()：无法获取mysqli

Question

我有一个问题，我无法从我的MySQL数据库中检索结果(通过PHP)。我在其他地方使用相同的函数，它可以完美地工作。然而，在这一点上，我一直收到"Warning: mysqli_query()：the‘t fetch mysqli“错误。下面解释了问题的详细信息。在我的PHP中，我在其他地方使用了一个非常类似的函数(getAllCountries，如下所示)，它确实工作得很好：

function getAllCountries()
{
    $result = db_query("SELECT countryid, name FROM country ORDER BY name ASC");

    echo "<select class=addresscountry name=country>";
    while($row = mysqli_fetch_array($result)) {
      echo '<option value="' . $row['countryid'] . '">' . $row['name'] . '</option>';
    }
    echo "</select>";

    mysqli_close(db_connect());
}

所以问题是这样的：

我有一个包含以下代码的php文件：

<?php
require 'includes/functions.php';

function getUserPicPath()
{
    $userid = $_SESSION['userid'];

    $result = db_query("SELECT picture FROM user WHERE userid='$userid'");

    while($row = mysqli_fetch_array($result)) {
        $picturepath = $row['picture'];
    }

    echo $picturepath;

    mysqli_close(db_connect());
}

我的functions.php文件包含以下行(以及其他不相关的函数)：

require 'dbfunctions.php';

我的dbfunctions.php是这样的：

<?php
function db_connect()
{
    require ".db_password.php";

    static $connection;

    if(!isset($connection)) {
        $connection = mysqli_connect('localhost',$username,$password,$dbname);
    }

    if($connection === false) {
        return mysqli_connect_error(); 
    }

    return $connection;
}

function db_query($query) 
{
    $connection = db_connect();

    $result = mysqli_query($connection,$query);

    return $result;
}

在我的PHP文档中，我调用了以下函数：

if ($userid == -1)
    {
        showNotAuthorizedPage();
    } else {
        myAccountPage();
    }

<div id="tabs-2">
    <p><?php getUserPicPath(); ?></p>
  </div>

我使用网页上的标签(http://jqueryui.com/tabs/#default)，这就是我想要调用它的地方。myAccountPage()函数产生以下错误：

Warning: mysqli_query(): Couldn't fetch mysqli in C:\Users\Dennis\Documents\My Dropbox\xxx\zzz\www\Project Files\includes\dbfunctions.php on line 29
Call Stack
#   Time    Memory  Function    Location
1   0.0000  256880  {main}( )   ..\myaccount.php:0
2   0.0010  283328  myAccountPage( )    ..\myaccount.php:181
3   0.0070  285368  getUserPicPath( )   ..\myaccount.php:121
4   0.0070  285528  db_query( ) ..\myaccount.php:11
5   0.0070  285624  mysqli_query ( )    ..\dbfunctions.php:29

( ! ) Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in C:\Users\Dennis\Documents\My Dropbox\me&roxy\WE\final project\Project Files\myaccount.php on line 13
Call Stack
#   Time    Memory  Function    Location
1   0.0000  256880  {main}( )   ..\myaccount.php:0
2   0.0010  283328  myAccountPage( )    ..\myaccount.php:181
3   0.0070  285368  getUserPicPath( )   ..\myaccount.php:121
4   0.0080  285768  mysqli_fetch_array ( )  ..\myaccount.php:13

( ! ) Notice: Undefined variable: picturepath in C:\Users\Dennis\Documents\My Dropbox\me&roxy\WE\final project\Project Files\myaccount.php on line 17
Call Stack
#   Time    Memory  Function    Location
1   0.0000  256880  {main}( )   ..\myaccount.php:0
2   0.0010  283328  myAccountPage( )    ..\myaccount.php:181
3   0.0070  285368  getUserPicPath( )   ..\myaccount.php:121

( ! ) Warning: mysqli_close(): Couldn't fetch mysqli in C:\Users\Dennis\Documents\My Dropbox\me&roxy\WE\final project\Project Files\myaccount.php on line 19
Call Stack
#   Time    Memory  Function    Location
1   0.0000  256880  {main}( )   ..\myaccount.php:0
2   0.0010  283328  myAccountPage( )    ..\myaccount.php:181
3   0.0070  285368  getUserPicPath( )   ..\myaccount.php:121
4   0.0100  285864  mysqli_close ( )    ..\myaccount.php:19

Answer 1

我认为这是因为当您第一次关闭数据库连接时，您忘记了：

unset($connection);

然后，当您再次尝试连接到数据库时，它会失败，因为它仍然设置为关闭的连接。

Answer 2

您忘记了包含您的数据库连接。只需将$connection添加到您的sql查询中：

function getAllCountries()
{
    $result = db_query($connection,"SELECT countryid, name FROM country ORDER BY name ASC");

    // enter code here
}