使用PHP从2个表中选择数据

Question

I am relatively new to PHP and SQL and I am creating a simple blog tool for my own page and I'm stuck on how I can make a comment section. I have 2 tables general, which contains the blog post and additional information comments, which contains comments

$servername = "localhost";
$username = "root";
$password = "password";
$dbname = "blog";
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error){
    die ("connection failed: " . $conn->connect_error);
}
$sql = "SELECT * FROM general WHERE hidden = 'false' ORDER BY id DESC";
$result = $conn->query($sql);
if ($result->num_rows > 0){
   while ($row = $result->fetch_assoc()){
     echo "<div class='blogpost'>
          <div class='blogbody'></div>";

     //I need to do a query into the comments table at this point to find
     //all comments matching the criteria to be matched with the post here.
     echo "<div class='comments'></div></div>";
   }
}
else{
    echo "no posts";
}

I manage to get the blogposts working but as soon as I try a second query by adding

$conn2 = new mysqli($servername, $username, $password, $dbname);
if ($conn2->connect_error){
    die ("connection failed: " . $conn2->connect_error);
}
$sql2 = "SELECT * FROM comments WHERE $row["parent"] ORDER BY id DESC";
$result2 = $conn2->query($sql2);
if ($result2->num_rows > 0){
    while ($row2 = $result2->fetch_assoc()){

    }
}
else{
    echo "no comments";
}

it all just breaks. I am not able to throw in a loop that gets all the comments for the specific post before it starts loading additional posts.

How would I go on about solving this? I might need a little spoonfeeding with comments in any code samples,

Answer 1

You can use the primary key of the post and that can be used in comments table as a foreign key so that you can easily make your query with that will show all the comments against that specific post. Then the query will be like this:

 $postid=$row['post_id'];

$sql2 = "SELECT * FROM comments WHERE post_id='$postid' ORDER BY post_id DESC";

Answer 2

Changing the second query to fixed the problem.

WHERE $row["parent"] ORDER. Change that to WHERE parent={$row['parent']} ORDER

Thanks to Jeff for providing this answer