Duplicate values in array from SQL query - PHP

I am querying a database for a list of activities which I wish to display in a month-view calendar matrix.  Obviously I don't want to make a query for each day of the month(!); so I have to split the results so that each day's activities can be looped separately as needed.

I now have a multidimensional array with sub-levels selected by day of the month - which is what I want.  However, this sub-array(?) shows all its values twice, each one against two keys, as this test output shows:

[acts] => Array
(
      [6] => Array
            (
                  [0] => 6
                  [day] => 6
                  [1] => 28244
                  [aid] => 28244
                  [2] => activity
                  [activityname] => activity
                  [3] => 28336
                  [enid] => 28336
            )

      [7] => Array
            (
                  [0] => 7
                  [day] => 7
                  [1] => 28245
                  [aid] => 28245
                  [2] => another activity
                  [activityname] => another activity
                  [3] => 28337
                  [enid] => 28337
            )

      [15] => Array
            (
                  [0] => 15
                  [day] => 15
                  [1] => 28246
                  [aid] => 28246
                  [2] => yet another activity
                  [activityname] => yet another activity
                  [3] => 28338
                  [enid] => 28338
            )

      [17] => Array
            (
                  [0] => 17
                  [day] => 17
                  [1] => 28247
                  [aid] => 28247
                  [2] => yet another activity still
                  [activityname] => yet another activity still
                  [3] => 28339
                  [enid] => 28339
            )

)

I suspect that this is why my attempt to display this data in the correct place on the matrix fails.

The original query, array reorganisation, and function to select the correct data (if any) for each day is this:

$sql = mysql_query("SELECT DAYOFMONTH(a.`date`) AS day, a.`aid`, a.`activityname`, u.`enid` FROM activities a JOIN user_entries u JOIN diaries d ON a.`aid` = u.`aid_FK` AND u.`did_FK` = d.`did` WHERE `mem_no_FK` = 2353 AND a.`date` BETWEEN '2009-07-01' AND '2009-08-01' ORDER BY `date`") or die ("<p>The system is currently unable to respond to your request. Please try later.</p>");

// Reorganise the events into an array keyed by day of the month
$acts = array();
while ($row = mysql_fetch_array($sql)) {
	if (!$acts[$row['day']]) $acts[$row['day']] = array();
	$acts[$row['day']] = $row;
}

//Insert activities for day in that day's cell
function insert_acts() {
	if ($acts[$day]) {
		foreach ($acts[$day] AS $row) {
			//Clean & display events
			$this_aid = htmlentities($row['aid']);
			$this_actname = htmlentities($row['activityname']);
			$this_enid = htmlentities($row['enid']);
			print "<div><a href=\"CPD_activity_details.php?aid=$this_aid\" class=\"\">$this_actname</a><br /><a href=\"CPD_activity_review.php?enid=$this_enid\" class=\"\">review</a></div>";
		}
		print "</td>";
	} else {
		print "</td>";
	}
}

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How can I fix this problem?