$sorgu = mysql_query("SELECT * FROM tablo");
$gunler = array();
while($veriler = mysql_fetch_assoc($sorgu)){
$id = $veriler['ID'};
$explode = explode(' ',$veriler['TARIH']);
$gun = $explode[0];
$saat = $explode[1];
$veri = $veriler['VERI'];
if(!isset($gunler[$gun])){ $gunler[$gun] = array(); }
$gunler[$gun][$saat] = $veri;
}

foreach($gunler as $gun => $saat){
Echo "Gün: $gun <br />";
foreach($saat as $key => $value){
echo $key."---".$value."<br />";
}}