AND post_id = %d
			  AND updated_date BETWEEN %s AND %s
			",
				$this->post_id,
				$this->get_date( $period, 'start' ),
				$this->get_date( $period, 'end' )
			)
		);// db call ok; no-cache ok.

	}

	/**
	 * Retrieve # of course enrollments within the period
	 *
	 * @since 3.15.0
	 * @since 3.31.0 Use $this->post_id instead of deprecated $this->course_id.
	 *
	 * @param string $period Optional. Date period [current|previous]. Default is 'current'.
	 * @return int
	 */
	public function get_enrollments( $period = 'current' ) {

		global $wpdb;

		return $wpdb->get_var(
			$wpdb->prepare(
				"
			SELECT DISTINCT COUNT( user_id )
			FROM {$wpdb->prefix}lifterlms_user_postmeta
			WHERE meta_value = 'yes'
			  AND meta_key = '_start_date'
			  AND post_id = %d
			  AND updated_date BETWEEN %s AND %s
			",
				$this->post_id,
				$this->get_date( $period, 'start' ),
				$this->get_date( $period, 'end' )
			)
		);// db call ok; no-cache ok.

	}

	/**
	 * Retrieve # of engagements related to the course awarded within the period
	 *
	 * @since 3.15.0
	 *
	 * @param string $type   Engagement type [email|certificate|achievement].
	 * @param string $period Optional. Date period [current|previous]. Default is 'current'.
	 * @return int
	 */
	public function get_engagements( $type, $period = 'current' ) {

		global $wpdb;

		$ids = implode( ',', $this->get_all_ids() );

		// phpcs:disable WordPress.DB.PreparedSQL.InterpolatedNotPrepared
		return $wpdb->get_var(
			$wpdb->prepare(
				"
			SELECT DISTINCT COUNT( user_id )
			FROM {$wpdb->prefix}lifterlms_user_postmeta
			WHERE meta_key = %s
			  AND post_id IN ( {$ids} )
			  AND updated_date BETWEEN %s AND %s
			",
				'_' . $type,
				$this->get_date( $period, 'start' ),
				$this->get_date( $period, 'end' )
			)
		);// db call ok; no-cache ok.
		// phpcs:enable WordPress.DB.PreparedSQL.InterpolatedNotPrepared

	}

	/**
	 * Retrieves and returns the number of lessons completed within the period.
	 *
	 * @since 3.15.0
	 * @since 5.10.0 Fixed issue when the course has no lessons.
	 *
	 * @param string $period Optional. Date period [current|previous]. Default is 'current'.
	 * @return int
	 */
	public function get_lesson_completions( $period = 'current' ) {

		global $wpdb;

		$lessons = implode( ',', $this->post->get_lessons( 'ids' ) );
		// phpcs:disable WordPress.DB.PreparedSQL.InterpolatedNotPrepared

		// Return early for courses without any lessons.