PHP - MySQL Weekly Sales Report Query Issue

I am preparing weekly sales report for particular seller so he can see after login at any time.

Current week info is collected using below code.

<?php 
$dt_week_start_date = date('Y-m-d 20:00:01',strtotime("last Saturday"));
$dt_week_end_date = date('Y-m-d 20:00:00',strtotime("next Saturday"));
?>

Below query is used to get sold item data for specific seller from table for current week. This query works fine if I simply display sold item listing on page.

<?php
$str_query_select = "SELECT * FROM t_product_purchase ";
$str_query_select .= " WHERE purchasedatetime BETWEEN '".$dt_week_start_date ."' AND '".$dt_week_end_date."'";
$str_query_select .= " AND sellerpkid=1";
$str_query_select .= " ORDER BY purchasedatetime DESC ";
?>

But I need to show sold items order wise like below. I tried to do GROUP BY on purchasedatetime field and tried few other things but it's not working at all. Please help me to solve this isse.

Purchase Date-Time       Product      Price
2014-08-10 14.20.00      Item 010      $50
2014-08-10 14.20.00      Item 016      $20
                         ------------------
                         Total :       $70
                         + Shipping :  $10
                         - Promo Code :$ 5
                         ------------------
                         Sub Total :   $75


2014-08-13 09.08.10      Item 056      $20
2014-08-13 09.08.10      Item 056      $65
2014-08-13 09.08.10      Item 056      $ 5
                         ------------------
                         Total :       $90
                         + Shipping :  $15
                         - Promo Code :$ 5
                         ------------------
                         Sub Total :   $100

Total For week 2014-08-09 to 2014-08-16 : $175

Data are stored in database table in following way. All data are related to single seller only.

• Buyer 01 buys 2 items together from site where shipping charge is $10 & promo code discount is $5 (so 2 records for 2 items are added in t_product_purchase table along with shipping charge and promo code discount)

• Buyer 02 buys 3 items together from site where shipping charge is $15 & promo code discount is $5 (so 3 records for 3 items are added in t_product_purchase table along with shipping charge and promo code discount)

Here is database table structure:

CREATE TABLE IF NOT EXISTS `t_product_purchase` (
`purchasepkid` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`sellerpkid` bigint(20) unsigned NOT NULL DEFAULT '0',
`productpkid` bigint(20) unsigned NOT NULL DEFAULT '0',
`prodcatpkid` bigint(20) unsigned NOT NULL DEFAULT '0',
`extendedprice` double(10,2) NOT NULL DEFAULT '0.00',
`shippingvalue` double(10,2) NOT NULL DEFAULT '0.00',
`discountpercentage` float(6,2) NOT NULL DEFAULT '0.00',
`discountamount` float(6,2) NOT NULL DEFAULT '0.00',
`finaldiscountedamount` float(6,2) NOT NULL DEFAULT '0.00',
`quantity` smallint(6) NOT NULL DEFAULT '0',
`color` varchar(255) DEFAULT NULL,
`size` varchar(255) DEFAULT NULL,
`emailid` varchar(255) NOT NULL DEFAULT '',
`firstname` varchar(100) DEFAULT NULL,
`lastname` varchar(100) DEFAULT NULL,
`address` varchar(255) DEFAULT NULL,
`city` varchar(100) DEFAULT NULL,
`state` varchar(100) DEFAULT NULL,
`country` varchar(100) DEFAULT NULL,
`zipcode` varchar(10) DEFAULT NULL,
`shippingaddress` text,
`specialnote` text,
`ipaddress` varchar(50) DEFAULT NULL,
`purchasedatetime` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`purchaseday` int(11) DEFAULT '0',
`purchasemonth` int(11) DEFAULT '0',
`purchaseyear` int(11) DEFAULT '0',
PRIMARY KEY (`purchasepkid`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;