Query to get 2 columns in same table

Question

I'm completely stuck on this bit of code and hoping someone can help. I have a database with one table called "pages" and it has 5 columns: id, file_name link_name, category, main_cat. Not sure if it matters but main_cat has type of tinytext and file_name is varchar.

id | file_name   | link_name   | category | main_cat 
1  | books       | Books       | books    | 1
2  | fiction     | Fiction     | books    | 2
3  | non-fiction | Non-Fiction | books    | 2
4  | music       | Music       | music    | 1
5  | alternative | Alternative | music    | 2
6  | country     | Country     | music    | 2

In my navigation menu(code below), I would like to have all of the main_cat(1) listed and then the sub-pages, man_cat(2) to show underneath. Here is the code I have, right now, I've tried many different ways including an inner join and left join but not matter what, I keep getting an error that says "Warning: mysqli_fetch_assoc() expects parameter 1 to be mysqli_result, boolean given in..."

<ul>
 <?php
   $query = "SELECT * FROM pages WHERE main_cat = 1 ORDER BY link_name ASC ";
   $main_pages = mysqli_query($conn, $query);
   confirm_query($main_pages);
 ?>
 <?php
   while($mainpage = mysqli_fetch_assoc($main_pages)) {
 ?>
  <li><a href="/edit.php?<?php echo $mainpage["id"]; ?>"><?php echo $mainpage["link_name"]; ?></a>  

  <?php
$query = "SELECT * FROM pages WHERE main_cat = 2 AND category = {$mainpage["file_name"]}";
$sub_pages = mysqli_query($conn, $query);
confirm_query($sub_pages);
  ?>
  <ul>
  <?php
while($subpage = mysqli_fetch_assoc($sub_pages)) {
  ?>
 <li><a href="/edit.php?<?php echo $subpage["id"]; ?>"><?php echo $subpage["link_name"]; ?></a></li>    
 <?php
}
 ?>
  <?php mysqli_free_result($sub_pages); ?>
   </ul>
 </li>
 <?php
}
 ?>
 <?php mysqli_free_result($main_pages); ?>
 </ul>      

Answer 1

This is going to give you heartburn:

$query = "SELECT * FROM pages WHERE main_cat = 2 AND category = {$mainpage["file_name"]}";

The problem is that the " characters around file_name are being interpreted as ending the string, and PHP is behaving unpredictably. In other words, PHP sees this:

$query = "SELECT * FROM pages WHERE main_cat = 2 AND category = {$mainpage["file_name"]}";
      // ^ start string                                                    ^ end     ^s ^end again

Try one of these options instead:

$query = "SELECT * FROM pages WHERE main_cat = 2 AND category = '{$mainpage['file_name']}'";
$query = "SELECT * FROM pages WHERE main_cat = 2 AND category = '".$mainpage["file_name"]."'";

Also, note the quotation marks around the variable -- unless file_name is actually a number, you need to enclose the data with quotation marks.

Finally, this probably goes without saying, but you really need to use prepared statements here.

Answer 2

Check if you have connected the right database and your queries are syntactically correct

$main_pages = mysqli_query($conn, $query); will return boolean if your $conn is not set up correctly or query syntax is wrong.

Hence when you fire mysqli_fetch_assoc($main_pages) it throws "Warning: mysqli_fetch_assoc() expects parameter 1 to be mysqli_result, boolean given in..." as, $main_pages is boolean value.

Answer 3

I think it is something to do with your second query, you may have it formatted wrong... I'm no expert but maybe someone else can edit if I have it wrong.

From this:

$query = "SELECT * FROM pages WHERE main_cat = 2 AND category = {$mainpage["file_name"]}";

To this:

$mainfilename = $mainpage['file_name'];

$query = "SELECT * FROM pages WHERE main_cat = 2 AND category = $mainfilename";