private function sql_joins() {

		global $wpdb;

		$joins = array();

		$fields = array(
			'first_name'       => "JOIN {$wpdb->usermeta} AS m_first ON u.ID = m_first.user_id AND m_first.meta_key = 'first_name'",
			'last_name'        => "JOIN {$wpdb->usermeta} AS m_last ON u.ID = m_last.user_id AND m_last.meta_key = 'last_name'",
			'overall_progress' => "JOIN {$wpdb->usermeta} AS m_o_p ON u.ID = m_o_p.user_id AND m_o_p.meta_key = 'llms_overall_progress'",
			'overall_grade'    => "JOIN {$wpdb->usermeta} AS m_o_g ON u.ID = m_o_g.user_id AND m_o_g.meta_key = 'llms_overall_grade'",
		);

		// Add the fields to the array of fields to select.
		foreach ( $fields as $key => $statement ) {
			if ( $this->requires_field( $key ) ) {
				$joins[] = $statement;
			}
		}

		$sql = implode( ' ', $joins );

		if ( $this->get( 'suppress_filters' ) ) {
			return $sql;
		}

		/**
		 * Filters the query JOIN clause
		 *
		 * @since 3.13.0
		 *
		 * @param string             $sql           The JOIN clause of the query.
		 * @param LLMS_Student_Query $student_query Instance of LLMS_Student_Query.
		 */
		return apply_filters( 'llms_student_query_join', $sql, $this );

	}