Show start date of current membership on the PMPro members list.

my_pmpro_memberslist_extra_cols_header_startdate.php

/*
	Show start date of current membership on the members list
	and members list CSV export.
	
	By default, PMPro will show the "Join Date" on the members list,
	which is the date the WP user was created. If you need to know
	the date the user upgraded to their current level, you can
	add this code to your active theme's functions.php or a custom plugin.
*/

//header
function my_pmpro_memberslist_extra_cols_header_startdate()
{
?>
<th>Started This Level</th>
<?php
}
add_action('pmpro_memberslist_extra_cols_header', 'my_pmpro_memberslist_extra_cols_header_startdate');

//column
function my_pmpro_memberslist_extra_cols_body_startdate($user)
{
	echo "<td>";

	$level = pmpro_getMembershipLevelForUser($user->ID);
	if(!empty($level) && !empty($level->startdate))
		echo date(get_option('date_format', $level->startdate));
	else
		echo "N/A";

	echo "</td>";
}
add_action('pmpro_memberslist_extra_cols_body', 'my_pmpro_memberslist_extra_cols_body_startdate');

//export header
function my_pmpro_members_list_csv_extra_columns_startdate($columns)
{
	$columns["membership_startdate"] = "my_extra_column_membership_startdate";
	
	return $columns;
}
add_filter("pmpro_members_list_csv_extra_columns", "my_pmpro_members_list_csv_extra_columns_startdate", 10);

//export column
function my_extra_column_membership_startdate($user)
{
	if(empty($user->membership_id))
		return "";
	
	global $wpdb;
		$startdate = $wpdb->get_var("SELECT UNIX_TIMESTAMP(startdate) as startdate FROM $wpdb->pmpro_memberships_users WHERE user_id = '" . $user->ID . "' AND membership_id = '" . $user->membership_id . "' ORDER BY id DESC LIMIT 1");
	
	if(!empty($startdate))
	{
		return date("Y-m-d", $startdate);
	}
	else
	{
		return "";
	}
}