WordPress/wp-admin/admin-db.php

<?php

function get_users_drafts( $user_id ) {
	global $wpdb;
	$user_id = (int) $user_id;
	$query = "SELECT ID, post_title FROM $wpdb->posts WHERE post_status = 'draft' AND post_author = $user_id ORDER BY ID DESC";
	$query = apply_filters('get_users_drafts', $query);
	return $wpdb->get_results( $query );
}

function get_others_drafts( $user_id ) {
	global $wpdb;
	$user = get_userdata( $user_id );
	$level_key = $wpdb->prefix . 'user_level';
	if ( 1 < $user->user_level ) {
		$editable = get_editable_user_ids( $user_id );
	
		if( !$editable ) {
				$other_drafts = '';
		} else {
			$editable = join(',', $editable);
			$other_drafts = $wpdb->get_results("SELECT ID, post_title FROM $wpdb->posts WHERE post_status = 'draft' AND post_author IN ($editable) AND post_author != '$user_id' ");
		}
	} else {
		$other_drafts = false;
	}
	return apply_filters('get_others_drafts', $other_drafts);
}

function get_editable_authors( $user_id ) {
	global $wpdb;
	$user = get_userdata( $user_id );
	$level_key = $wpdb->prefix . 'user_level';

	if ( 7 > $user->user_level ) // TODO: ROLE SYSTEM
		return false;

	$editable = get_editable_user_ids( $user_id );

	if( !$editable )
			return false;
	else {
		$editable = join(',', $editable);
		$authors = $wpdb->get_results( "SELECT * FROM $wpdb->users WHERE ID IN ($editable)" );
	}

	return apply_filters('get_editable_authors', $authors);
}

function get_editable_user_ids( $user_id, $exclude_zeros = true ) {
	global $wpdb;
	$user = get_userdata( $user_id );
	$level_key = $wpdb->prefix . 'user_level';

	$query = "SELECT * FROM $wpdb->usermeta WHERE meta_key = '$level_key'";
	if ( $exclude_zeros )
		$query .= " AND meta_value != '0'";
	$possible = $wpdb->get_results( $query );

	if ( !$possible )
		return false;	

	$user_ids = array();
	foreach ( $possible as $mark )
		if ( intval($mark->meta_value) <= $user->user_level )
			$user_ids[] = $mark->user_id;
	if ( empty( $user_ids ) )
		return false;
	return $user_ids;
}

function get_author_user_ids() {
	global $wpdb;
	$level_key = $wpdb->prefix . 'user_level';

	$query = "SELECT user_id FROM $wpdb->usermeta WHERE meta_key = '$level_key' AND meta_value != '0'";

	return $wpdb->get_col( $query );
}

function get_nonauthor_user_ids() {
	global $wpdb;
	$level_key = $wpdb->prefix . 'user_level';

	$query = "SELECT user_id FROM $wpdb->usermeta WHERE meta_key = '$level_key' AND meta_value = '0'";

	return $wpdb->get_col( $query );
}

?>