基于PHP中的其他值循环遍历值

I have the following SQL to fetch from a WordPress database outside WordPress:

SELECT p.post_name, m.meta_key, m.meta_value FROM wp_postmeta m INNER JOIN wp_posts p ON m.post_id = p.post_name WHERE p.post_type = 'something' LIMIT 0, 100;

post_name in wp_posts contains an id for the specific post, and matches post_idin wp_postmeta. meta_key contains field names, such as date, place, etc. meta_value contains the values for each of these fields.

So each post has a set of fields (meta_key) that each have a value (meta_value).

I'm trying to loop through these for each post, but nothing I've tried has worked. For now I have this, which shows all the data, but it loops through the meta_values instead of showing the meta_values for each post_id.

$data = $result->fetch_assoc();
if ($result = mysqli_query($conn, $sql)) {
  while ($row = $result->fetch_assoc()) { ?>
  <li>
  <?php
    echo $row["meta_value"];        
  ?>  
  </li>
  <?php
    } $result->close();
  }
  ?>

This sort of gives me:

<li>Post 1, meta value 1</li>
<li>Post 1, meta value 2</li>
<li>Post 2, meta value 1</li>
<li>Post 2, meta value 2</li>

But I need

<li>Post 1, meta value 1 — Post 1, meta value 2</li>
<li>Post 2, meta value 1 — Post 2, meta value 2</li>

Do you have any ideas?

Update based on comment from @ChristianF. foreach didn't work, so I tried using while instead.

The results are somewhat weird, where it seems eg. meta value 1 from post 1 is repeated lots of times. There are lots of empty <li> elements as well, so I'm guessing the code somehow prints a <li> element for each row with the post_id, even though not all meta_values need to be printed. I've included a couple of them using if statements. I've inserted the generated HTML below the code.

while ($row = $result->fetch_array()) {
if (!isset ($oldID)) {
    $oldID = $row['post_id'];
}

if ($oldID != $row['post_id']) {
    // Removing the last 3 characters from the output,
    // as we don't have any more items after this one.
    $postOut = substr ($postOut, 0, -4)."</li>
<li>";
}

if ($row['meta_key'] == 'who_what') {
    $postOut .= $row['meta_value'];
} else if ($row['meta_key'] == 'place') {
    $postOut .= $row['meta_value'];
}

echo $postOut;
}

The result is huge, and it also seems to cut off some of the values. I haven't included the entire result.

<li></li>
</li>
<li></li>
</li>
</li>
<li>Meta_value from who_what key</li>
</li>
</li>
<li></li>
<li></li>
</li>
</li>
<li></li>
</li>
<li>Full meta_value from place key</li>
</li>
</li>
<li></li>
</li>
<li>Meta_value from place key missing last four characters</li>
<li></li>
</li>
</li>
<li></li>
</li>
<li>Meta_value from place key missing last four characters</li>
</li>
<li></li>
</li>
</li>
<li></li>
</li>
<li>Meta_value from place key missing last four characters</li>
</li>
</li>
<li></li>
</li>
</li>
<li></li>

You need to have a variable, in which you're storing the post ID. Then check this for each row, and if it's different from the current one print a new row.
Something like this in other words:

// Start output with a list element.
$postOutput = '<li>':

foreach ($res->fetchArray () as $row) {
    // Prime the old ID, so that we can check against it later on.
    if (!isset ($oldID)) {
        $oldID = $row['post_id'];
    }

    // First, we need to end the old list item if we have a new post.
    if ($oldID != $row['post_id']) {
        // Removing the last 3 characters from the output,
        // as we don't have any more items after this one.
        $postOut = substr ($postOut, 0, -3)."</li>
<li>";
    }

    // Adding the list element with the expectation of more
    // content to be atted to it later on.
    $postOut .= "Post #, meta ".$row['meta'].' - ';
}