Nesting foreach loops with PDO statements - php

Question

I'm trying to nest foreach loops with PDO statements (this previously worked for me in mysql,btw). The first example works and the second one doesn't. However I'd prefer not to run a SQL query every time (isn't that the point of PDO?) and would prefer to use something more like example 2. However, it doesn't 'nest' the loop inside the other, it seems, rather it runs the first then the next.
Example 1)
foreach($db->query('SELECT country FROM db GROUP BY `country`') as $row1) {
echo $row1['country']."<br/>";
foreach($db->query('SELECT * FROM db') as $row2) {
if ($row1['country']==$row2['country']){
echo $row2['name']."<br/>";
}
}
}
Example 2)
$cntry = $db->query('SELECT country FROM db GROUP BY `country` ');
$rslts = $db->query('SELECT * FROM db');
foreach ($cntry as $row1) {
echo "<div id='".$row1['country']."'>".$row1['country']."<br/>";
foreach($rslts as $row2) {
if ($row1['country']==$row2['country']){
echo $row2['name']."<br/>";
}
};
echo "</div>";
}

Answer 1

(isn't that the point of PDO?)
No. The point of PDO is to send your query to database server and to return the results back. But PDO cannot reduce the number of queries executed.
So, here goes the proper solution:
$stmt = $db->query('SELECT country, name FROM db ORDER BY country, name');
$data = $stm->fetchAll(PDO::FETCH_COLUMN|PDO::FETCH_GROUP);
foreach ($data as $country => $row)
{
echo $country."<br/>\n";
foreach ($row as $name)
{
echo $name."<br/>\n";
}
}
As a matter of fact, fetchAll() is just a syntax sugar for the code like this:
$data = array();
while ($row = $stmt->fetch())
{
$data[] = $row;
}
it just creates a regular PHP array out of query result. And of course you can loop over this array as many times as you wish. Means you an always replace fetchAll() with manual looping over results, and of course you may group the results whatever way you wish.
While using foreach on $stmt is just a syntax sugar again, intended to confuse PHP users. Because $stmt is not an array but a way more complex structure.

Answer 2

not sure, but as I remember it would be like this
$cntry = $db->query('SELECT country FROM db GROUP BY `country` ')->fetchAll (PDO::FETCH_COLUMN);
$rslts = $db->query('SELECT * FROM db')->fetchAll(PDO::FETCH_COLUMN);
foreach ($cntry as $row1) {
echo $row1['country']."<br/>";
foreach($rslts as $row2) {
if ($row1['country']==$row2['country']){
echo $row2['name']."<br/>";
}
}
}