How to compare EST date time with mysql data - php

Question

I have purchase data in mysql database table. All data on server are stored in UTC timezone.
I can convert date-time in EST timezone using below code.
$date = date_create(date('Y-m-d H:i:s'), timezone_open('Etc/GMT+0'));
date_timezone_set($date, timezone_open('Etc/GMT+5'));
I am getting last and next Saturday of current day using below code.
$dt_week_start_time = strtotime("last saturday")+((20*3600)+ 1);
$dt_week_start_date = date('Y-m-d G:i:s', $dt_week_start_time);
$dt_week_end_time = $dt_week_start_time + (7*3600*24) - 1;
$dt_week_end_date = date('Y-m-d G:i:s', $dt_week_end_time);
But how can i compare above EST timezone converted date-time with mysql data stored in UTC timezone? I need to convert data of 'purchasedatetime' field in EST timezone when I fire below query. Is this possible? Or am I doing it in wrong way? Please advise.
$str_query_select = "SELECT *, SUM(extendedprice) AS gross_price 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 .= " GROUP BY purchasedatetime ORDER BY purchasedatetime DESC ";

Answer 1

You can see this:
http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#function_convert-tz
or
SET time_zone = 'proper timezone';
being done once right after connect to database. and after this all timestamps will be converted automatically when selecting them.
in php you can do this:
$date = new DateTime($dt_week_start_date);
$date->setTimezone(new DateTimeZone('Europe/Moscow')); // based on your required zone
echo $date->format('Y-m-d H:i:s');
then use it in your sql.