将多个表连接在一起

I am trying to join two tables together. In posts table I have two column post_id and post_message.

In another table name post_attach have row_id, postid(same as post_id), and file_name( As like ms.jpg).

A post may have several attachment.But I don't know what will be query to show a post with several attachment. Here is my query...

$s = " SELECT posts.post_id,post_message, post_attach.file_name from posts join post_attach on post_id=row_id;

<?php

$conn = mysqli_connect('localhost', 'root', 'root', 'blog') or die();


?>

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Document</title>
    </head>
    <body>
        <h3>Allo post with their attahcment</h3>
        <?php 
            $s = " SELECT posts.post_id,post_message, post_attach.file_name from posts join post_attach on post_id=row_id;
";
            $q = mysqli_query($conn,$s);


            while ($row = mysqli_fetch_array($q)) {?>
                <p>Post No: <?php echo $row['post_id'] ?></p>
                <p>Post text: <?php echo $row['post_message'] ?></p>
                <p>Post attach: <?php echo $row['file_name'] ?></p>
            <?php } ?>
    </body>
</html>

I want something like:

post no: 1, post text: hello php, attachment: ms.jpg, ms.jpeetc.

The final word is every post will show with their relative attachment.

I wouldn't join the tables outright. I would iterate through the main posts table and show the post id and post message, then loop through the attachments. Something like:

<?php 
$s = "SELECT posts.post_id,post_message FROM posts";
$q = mysqli_query($conn,$s);

while($row = mysqli_fetch_array($q))
{
    ?>
    <p>Post No: <?php echo $row['post_id'] ?></p>
    <p>Post text: <?php echo $row['post_message'] ?></p>
    <p>
        Post attach:
        <?php
        $att = "SELECT post_attach.file_name FROM post_attach WHERE post_id = $row[post_id]";
        $files = mysqli_query($conn,$att);
        while($row_files = mysqli_fetch_array($files))
        {
            echo $row_files['file_name'] . "<br>";
        }
        ?>
    </p>
    <?php
}
?>