SQL não retorna a nada

WHERE transaction_status = 'completed' 

<?php

$actual_week = date('w');

switch ($actual_week) {
	case '0':
		$day_before = 6;
		$day_after = 0;
		break;
	case '1':
		$day_before = 0;
		$day_after = 6;
		break;
	case '2':
		$day_before = 1;
		$day_after = 5;
		break;
	case '3':
		$day_before = 2;
		$day_after = 4;
		break;
	case '4':
		$day_before = 3;
		$day_after = 3;
		break;
	case '5':
		$day_before = 4;
		$day_after = 2;
		break;
	
	default:
		$day_before = 5;
		$day_after = 1;
		break;
}

$start_day = date("Y-m-d 00:00:00");

$end_day = date("Y-m-d 59:59:59");

$start_week = date("Y-m-d 00:00:00", strtotime("$start_day -$day_before days"));

$end_week =  date("Y-m-d 59:59:59", strtotime("$end_day $day_after days"));;

$start_month = date('Y-m-1 00:00:00');

$end_month = date('Y-m-t 59:59:59');

$sql_pay_day = "SELECT SUM(transaction_amount) total 
				FROM tbl_credit_card_transactions 
				WHERE transaction_datetime
				BETWEEN '$start_day' AND '$end_day'";

$query_pay_day = mysql_query($sql_pay_day);

$result_pay_day = mysql_fetch_row($query_pay_day); 

$sql_pay_week = "SELECT SUM(transaction_amount) total 
				FROM tbl_credit_card_transactions 
				WHERE transaction_datetime
				BETWEEN '$start_week' AND '$end_week'";

$query_pay_week = mysql_query($sql_pay_week);

$result_pay_week = mysql_fetch_row($query_pay_week); 

$sql_pay_month = "SELECT SUM(transaction_amount) total 
				FROM tbl_credit_card_transactions 
				WHERE transaction_datetime
				BETWEEN '$start_month' AND '$end_month'";

$query_pay_month = mysql_query($sql_pay_month);

$result_pay_month = mysql_fetch_row($query_pay_month); 

?>

<?php echo $result_pay_day[0]; ?>
<?php echo $result_pay_week[0]; ?>
<?php echo $result_pay_month[0]; ?>