PHP MySQL Display One Time - php

Question

I have two tables called categories and topics.
categories has columns category_id and category_title. topics has columns topic_id, topic_title, and category_id.
I currently display the columns like so:
$result = mysqli_query($db_server, 'SELECT c.category_title, t.topic_title FROM categories c JOIN topics t on c.category_id = t.category_id');
while ($row = mysqli_fetch_array($result))
{
$category_title[] = $row['category_title'];
$topic_title[] = $row['topic_title'];
}
<?php
foreach ($category_title as $category_title):
echo htmlspecialchars($category_title, ENT_QUOTES, 'UTF-8');?><br />
<?php endforeach; ?>
<?php
foreach ($topic_title as $topic_title):
echo htmlspecialchars($topic_title, ENT_QUOTES, 'UTF-8');?><br />
<?php endforeach; ?>
This will display as:
Category 1
Category 1
Category 2
Topic 1
Topic 2
Topic 3
Topic 1 and 2 are assigned to Category 1, while Topic 3 is assign to Category 2.
How can I have Category display once if there are multiple topics assign to it, such as:
Category 1
Category 2
Topic 1
Topic 2
Topic 3
Please no classes and objects examples. I'm not learning that yet.

Answer 1

You can run query two time first for category then run new query to selected topic according to category as below:
<?php
$result = mysqli_query($db_server, 'SELECT c.category_id,c.category_title FROM categories as c');
$recordArray=array();
while ($row = mysqli_fetch_array($result))
{
$category_id = $row['category_id'];
$recordArray[$category_id] = $row['category_title'];
//Query For Topic
$getTopic = mysqli_query($db_server, "SELECT t.topic_title FROM topics as t WHERE t.category_id='".$category_id."'");
while ($getRow = mysqli_fetch_array($getTopic))
{
$recordArray[$category_id]['topic'][] = $getRow['topic_title'];
}
}
print"<pre>";
print_r($recordArray);
?>

Answer 2

Use group_concat, here is an example http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

Answer 3

You can modify your SQL query adding a "GROUP BY" statement. It would be something like:
SELECT c.category_title, t.topic_title FROM categories c JOIN topics t on c.category_id = t.category_id GROUP BY c.category_id
You can find here a clear example of using GROUP BY.

Answer 4

written off my head not tested:
first I dunno why don't you use it inside one loop, it will perform faster but it will swap the output
$result = mysqli_query($db_server, 'SELECT c.category_title, t.topic_title FROM categories c JOIN topics t on c.category_id = t.category_id');
$oldCategory='';
while ($row = mysqli_fetch_array($result)) {
if ($oldCategory!=$row['category_title']) {
echo htmlspecialchars($row['category_title'], ENT_QUOTES, 'UTF-8').'<br />';
$oldCategory=$row['category_title'];
}
echo htmlspecialchars($row['topic_title'], ENT_QUOTES, 'UTF-8').'<br />';
}
or this will not swap the output:
$result = mysqli_query($db_server, 'SELECT c.category_title, t.topic_title FROM categories c JOIN topics t on c.category_id = t.category_id');
$oldCategory='';
$catStr='';
$topStr='';
while ($row = mysqli_fetch_array($result)) {
if ($oldCategory!=$row['category_title']) {
$catStr.=htmlspecialchars($row['category_title'], ENT_QUOTES,'UTF-8').'<br />';
$oldCategory=$row['category_title'];
}
$topStr.=htmlspecialchars($row['topic_title'], ENT_QUOTES, 'UTF-8').'<br />';
}
echo $catStr.$topStr;