how do I pass the value form the sdate form input on line 20 into the sql query on line 85

membershipquery.php

<?php
/*
Plugin Name: Member payment report
Plugin URI: http://www.michiganjaycees.org
Description: this is a report showing the payments that have processed
Author: Dan Moellering
Version: .1
Author URI: http://mdmnow.com
*/
add_action('admin_menu', 'member_payment_report_action');
function member_payment_report_action () {
	add_options_page('MemberPaymentReport', 'MemberPaymentReport', 'manage_options', __FILE__, 'memberPayment_admin');
}
function memberPayment_admin()
{
	?>
	<div class="wrap">
	<h4>Membership Report</h4> 
	<form action="" method="POST">
		<input type="date" name="sdate" value="pick-date" />
		<input type="submit" name="search_orders" value="Search" class="button-primary" />
	</form>
	<br />
	<table class="widefat">
		<thead>
			<tr>
				<th>ID</th>
				<th>Timestamp</th>
				<th>User login</th>
				<th>User email</th>
				<th>Level</th>
				<th>Total</th>
				<th>Last name</th>
				<th>First name</th>
				<th>Address</th>
				<th>City</th>
				<th>State</th>
				<th>Zip</th>
				<th>DOB</th>
				<th>Phone</th>
			</tr>
		</thead>
		<tfoot>
			<tr>
				<th>ID</th>
				<th>Timestamp</th>
				<th>User login</th>
				<th>User email</th>
				<th>Level</th>
				<th>Total</th>
				<th>Last name</th>
				<th>First name</th>
				<th>Address</th>
				<th>City</th>
				<th>State</th>
				<th>Zip</th>
				<th>DOB</th>
				<th>Phone</th>
			</tr>
		</tfoot>
		<tbody>
			<?php 
			global $wpdb;
			$memberquery = array();
			if (isset($_POST['search_orders'])) {

			$memberquery = $wpdb->get_results(
				"
				SELECT 
				o.user_id as user_id,
				o.timestamp as timestampID,
				(select user_login from wp_users where id = o.user_id limit 1) as user_login,
				(select user_email from wp_users where id = o.user_id limit 1) as user_email,
				(select name from wp_pmpro_membership_levels where id = o.membership_id limit 1) as level,
				o.total as total,
				(select meta_value from wp_usermeta where user_id = o.user_id and meta_key = 'pmpro_slastname' limit 1) as last_name,
				(select meta_value from wp_usermeta where user_id = o.user_id and meta_key = 'pmpro_sfirstname' limit 1) as first_name,
				(select meta_value from wp_usermeta where user_id = o.user_id and meta_key = 'pmpro_saddress1' limit 1) as address,	
				(select meta_value from wp_usermeta where user_id = o.user_id and meta_key = 'pmpro_scity' limit 1) as city,
				(select meta_value from wp_usermeta where user_id = o.user_id and meta_key = 'pmpro_sstate' limit 1) as state,
				(select meta_value from wp_usermeta where user_id = o.user_id and meta_key = 'pmpro_szipcode' limit 1) as zip,	
				(select meta_value from wp_usermeta where user_id = o.user_id and meta_key = 'dob' limit 1) as dob,	
				(select meta_value from wp_usermeta where user_id = o.user_id and meta_key = 'phone' limit 1) as phone
				FROM wp_pmpro_membership_orders o
				WHERE o.status = 'success' AND o.timestamp > 'sdate'
				ORDER BY timestamp DESC;
				"
			);
			update_option('membership_payment_memberquery', $memberquery ); //store the results in wp options table
			}
			else if (get_option('membership_payment_memberquery'))
			{
				$memberquery = get_option('membership_payment_memberquery');
			}
				foreach ($memberquery as $memberquery) {
					?>
					<tr>
					<?php 

					echo '<td><a href="http://michiganjaycees.org/wp-admin/user-edit.php?user_id='.$memberquery->user_id.'" target="_blank">'.$memberquery->user_id.'</a></td>';
					//echo "<td>".$memberquery->user_id."</td>";
					echo "<td>".$memberquery->timestampID."</td>";
					echo "<td>".$memberquery->user_login."</td>";
					echo "<td>".$memberquery->user_email."</td>";
					echo "<td>".$memberquery->level."</td>";
					echo "<td>".$memberquery->total."</td>";
					echo "<td>".$memberquery->last_name."</td>";
					echo "<td>".$memberquery->first_name."</td>";
					echo "<td>".$memberquery->address."</td>";
					echo "<td>".$memberquery->city."</td>";
					echo "<td>".$memberquery->state."</td>";
					echo "<td>".$memberquery->zip."</td>";
					echo "<td>".$memberquery->dob."</td>";
					echo "<td>".$memberquery->phone."</td>";

					?>
					</tr>
					<?php
				}
			  ?>
		</tbody>
</div>
<?php
}
?>