警告：mysqli_num_rows（）期望参数1为mysqli_result，在/ Users /中给出null

Question

有人可以帮忙吗？ 我被要求从champs和teamstats表中挑选团队，teamid，pennants和worldseries专栏。并在champs表中打印棒球队的数量。我有2个文件如下。我不停地收到警告：警告：mysqli_num_rows（）期望参数1为mysqli_result，在/ Users /

中给出null

<?php //FIRST FILE: mysqli_connect.php

DEFINE ('DB_USER', 'happy');
DEFINE ('DB_PASSWORD', 'xxxx');
DEFINE ('DB_HOST', 'localhost');
DEFINE ('DB_NAME', 'baseball_stats');

// Make the connection:
 $dbc = @mysqli_connect (DB_HOST, DB_USER, DB_PASSWORD, DB_NAME) OR 
 die ('Could not connect to
 MySQL: ' . mysqli_connect_error() );

 // Set the encoding...
 mysqli_set_charset($dbc, 'utf8');
 ?>
 //// SECOND FILE 
 <?php

require ('a9mysqli_connect.php');

$query = "SELECT t.team AS T, t.team_id AS Ti, c.pennants AS P, 
c.worldseries AS W from `teamstats` as t join `champs` as c on 
t.team_id = c.team_id;";

 $result = @mysqli_query ($dbc, $query); 

 // Count the number of returned rows:
$num = mysqli_num_rows($result);
//Create an HTML table for displaying the query results:

if ($num > 0) {  // If it ran OK, display the records.
echo "<p>There are currently $num baseball teams.</p>"; 

echo '<table align="center">
<tr>
<td align="left"><b>Team</b></td>
<td align="right"><b>Team ID</b></td>
<td align="right"><b>Pennants </b></td>
<td align="right"><b>WorldSeries </b></td>
</tr>'
;
//Fetch and print each returned record:

while ($row = mysqli_fetch_array ($result, MYSQLI_ASSOC)) {
echo '<tr><td align="left">' . $row['T'] . '</td><td align= "left">' . 
$row['Ti'] . '</td><td align= "left">' . $row['P'] . '</td><td align= 
"left">' . $row['W'] . '</td></tr>'; 
 }
 echo '</table>';
mysqli_free_result ($result);
}
else { //If it didnot run OK.

 // Public message:
 echo '<p class="error"> There are currently no baseball teams in
 the database.</p>';
  echo '<p>' . mysqli_error($dbc) . '<br /><br />Query: ' . $query . 
  '</p>';
 }
 mysqli_close($dbc); // Close the database connection.
?>

Answer 1

mysqli_query对于成功的查询，它将返回TRUE，失败时为FALSE，您需要在代码检查中检查查询是否成功 if ($result)

<强>更新

这是因为您使用在另一个文件$dbc

中声明的mysqli_connect.php

<?php //FIRST FILE: mysqli_connect.php

DEFINE('DB_USER', 'happy');
DEFINE('DB_PASSWORD', 'xxxx');
DEFINE('DB_HOST', 'localhost');
DEFINE('DB_NAME', 'baseball_stats');

// Make the connection:
$dbc = @mysqli_connect(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME) OR
die ('Could not connect to
 MySQL: ' . mysqli_connect_error());

// Set the encoding...
mysqli_set_charset($dbc, 'utf8');
?>

然后在第二个php文件中，你需要像require ('a9mysqli_connect.php');这样的文件，这个文件不存在。运行代码，因为它有以下错误。

错误很明显，您将一个不存在的变量传递给mysqli_query，您需要正确地要求该文件。

<?php

require('mysqli_connect.php');
$query = "SELECT t.team AS T, t.team_id AS Ti, c.pennants AS P, 
c.worldseries AS W from `teamstats` as t join `champs` as c on 
t.team_id = c.team_id;";
$result = mysqli_query($dbc, $query); // remove @
if ($result) {
    // Count the number of returned rows:
    $num = mysqli_num_rows($result);
    //Create an HTML table for displaying the query results:

    if ($num > 0) {  // If it ran OK, display the records.
        echo "<p>There are currently $num baseball teams.</p>";

        echo '<table align="center">
                <tr>
                    <td align="left"><b>Team</b></td>
                    <td align="right"><b>Team ID</b></td>
                    <td align="right"><b>Pennants </b></td>
                    <td align="right"><b>WorldSeries </b></td>
                </tr>';
        //Fetch and print each returned record:

        while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
            echo '<tr><td align="left">' . $row['T'] . '</td><td align= "left">' . $row['Ti'] . '</td><td align= "left">' . $row['P'] . '</td><td align="left">' . $row['W'] . '</td></tr>';
        }
        echo '</table>';
        mysqli_free_result($result);
    } else { //If it didnot run OK.

        // Public message:
        echo '<p class="error"> There are currently no baseball teams in the database.</p>';
        echo '<p>' . mysqli_error($dbc) . '<br /><br />Query: ' . $query .
            '</p>';
    }
    mysqli_close($dbc); // Close the database connection.
} else {
    echo 'Something wrong happened!!!';
}

Answer 2

1. 在“描述”下的php.net上查看mysqli_query：

  

对于非DML查询（不是INSERT，UPDATE或DELETE），此函数是   类似于调用mysqli_real_query（）后跟任一个   mysqli_use_result（）或mysqli_store_result（）。

1. 请参阅php.net下的“返回值”下的mysqli_store_result：

  

此函数之后返回FALSE的可能原因   成功调用mysqli_query（）可能会导致结果集太大（内存   因为它无法分配）。如果mysqli_field_count（）返回一个   非零值，该语句应该产生非空结果   集。

我还写了一个左连接sql查询，也许你可以使用它。您使用了 JOIN 关键字。我使用 LEFT JOIN 。但我也测试了 JOIN 。它工作正常，所以你的查询还可以。

<强> 描述 ： 阅读所有团队（来自团队表），并为每个团队，还有相应的冠军细节（来自 champs 表的三角旗和世界系列）。但是只有team_id也在冠军队伍中的球队存在（ISNULL(c.team_id) = FALSE）。

SELECT 
    t.team AS T,
    t.team_id AS Ti,
    c.pennants AS P,
    c.worldseries AS W
FROM
    `teamstats` AS t
        LEFT JOIN
    `champs` AS c ON t.team_id = c.team_id
WHERE
    ISNULL(c.team_id) = FALSE
;