<?php
$dbLink = new mysqli('host', 'user', 'pwd', 'db');
 
$result = $dbLink->query("... Put your query here ...");
if($result)
{
    $data = array();
 
    // Loop through all the returned rows and group the values
    // into the $data array based on the 'col2' field.
    while($row = $result->fetch_assoc($result)
    {
        $data[$row['col2']][] = $row['col1'];
    }
 
    // Loop through the 'col2' values and print a list of
    // 'col1' values for each of them.
    foreach($data as $_col2 => $_col1_list)
    {
        echo "----\n{$_col2}\n----\n";
        foreach($_col1_list as $_col1)
        {
            echo $_col1, "\n";
        }
    }
}
else
{
    echo "Your query phailed! " . $dbLink->error;
}
?>