php - 嵌套 mysqli_query 没有返回结果

Question

在下面的代码中，我需要回显子查询的结果。当我回显$row['email'].'<br>';时 echo 工作正常，我收到了所有电子邮件。

问题在于:

$resultsub.echo $rowb["email"];

为空

问题:我在子查询 $resultsub 中做错了什么？

$result = mysqli_query($conn, "SELECT * FROM wp_mm_email_bounces");

if ($result) {
// output data of each row
while( $row = mysqli_fetch_assoc( $result ) )
        {
            echo $row['email'].'<br>'; // echo works okay
            $resultsub =  mysqli_query($conn, "SELECT * FROM `wp_mm_external_emails` WHERE `email` = '". $row['email'] ."' "); 
            // when I echo this subquery it runs ok. but somehow I get an empty
            while( $rowb = mysqli_fetch_assoc( $resultsub) )
            {
                echo $rowb["email"];
        } else {
            echo "0 $resultsub";
            }
} else {
echo "0 results";
}

Answer 1

我认为你以某种方式搞乱了你的 if-else 和 while 部分。如果我“漂亮地打印”上面的代码片段，它看起来像这样(请参阅我的评论):

<?php
$result = mysqli_query($conn, "SELECT * FROM wp_mm_email_bounces");

if ($result) 
{
    while( $row = mysqli_fetch_assoc( $result ) )
    {
        echo $row['email'].'<br>';
        $resultsub =  mysqli_query($conn, "SELECT * FROM `wp_mm_external_emails` WHERE `email` = '". $row['email'] ."' "); 

        while( $rowb = mysqli_fetch_assoc( $resultsub) )
        {
            echo $rowb["email"];
        } 
        else //Where is the corresponding if?
        {
            echo "0 $resultsub";
        }
    }
} //I added this enclosing bracket to the if-statement

else //If this is the corresponding else of your first if at the beginning, then you never closed it
{
    echo "0 results";
}

?>