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

my-pmpro-memberslist-extra-cols-header-startdate.php

<?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 '';
	}
}