Join two MySQL tables and group result with php - php

Question

I have the following code to populate cities in a table.
$cities_query = "SELECT city_name FROM city_selection";
$cities_result = mysql_query($cities_query);
echo "<table>";
while ($row = mysql_fetch_assoc($cities_result))
{
echo "<tr>";
echo "<td>".$row['city_name'] . "</td>";
echo "</tr>";
}
echo "</table>";
Now I need to group every city by a region so I created the table called city_region_selection and added a Foreign key from the new column "region_id" in the city_selection table to region_id in the new table.
I'm now struggling to present this data in a nice html table using PHP.
Is it even possible to populate first a table row with region_name and then some subrows containing cities from that region? Please see this image for details:

Answer 1

You just have to do a little preprocessing:
/* SQL
SELECT
city_name,
region_name
FROM
city_selection
NATURAL JOIN city_region_selection
SQL */
$regions = array();
while ($result->fetch()) {
if (!isset($regions[$result->region_name])) {
$regions[$result->region_name] = array();
}
$regions[$result->region_name][] = $result->city_name;
}
Alternate Method with SQL focus
/* SQL
SELECT
region_name,
GROUP_CONCAT(city_name SEPARATOR ',') cities
FROM
city_selection
NATURAL JOIN city_region_selection
GROUP BY
region_name
*/
$regions = array();
while ($result->fetch()) {
$regions[$result->region_name] = explode(',', $result->city_name);
}
Help
Note that the while syntax is just abridged. You would probably replace it with
while ($row = mysql_fetch_assoc($cities_result)) {
$regions[$row['region_name']] = explode(',', $row['city_name']);
}
... for example
Once regions is built, simply do this:
foreach ($regions as $region => $cities) {
echo "<tr><td>$region</td></tr>";
foreach ($cities as $city) {
echo "<tr><td class="tabbed">$city</td></tr>";
}
}