}

	/**
	 * Maps ordering specified by the user to columns in the database/fields in the data.
	 *
	 * @param string $order_by Sorting criterion.
	 * @return string
	 */
	protected function normalize_order_by( $order_by ) {
		global $wpdb;

		if ( 'tax_code' === $order_by ) {
			return 'CONCAT_WS( "-", NULLIF(tax_rate_country, ""), NULLIF(tax_rate_state, ""), NULLIF(tax_rate_name, ""), NULLIF(tax_rate_priority, "") )';
		} elseif ( 'rate' === $order_by ) {
			return "CAST({$wpdb->prefix}woocommerce_tax_rates.tax_rate as DECIMAL(7,4))";
		}

		return $order_by;
	}

	/**
	 * Create or update an entry in the wc_order_tax_lookup table for an order.
	 *
	 * @param int $order_id Order ID.
	 * @return int|bool Returns -1 if order won't be processed, or a boolean indicating processing success.
	 */
	public static function sync_order_taxes( $order_id ) {
		global $wpdb;

		$order = wc_get_order( $order_id );
		if ( ! $order ) {
			return -1;
		}

		$tax_items   = $order->get_items( 'tax' );
		$num_updated = 0;

		foreach ( $tax_items as $tax_item ) {
			$result = $wpdb->replace(
				self::get_db_table_name(),
				array(
					'order_id'     => $order->get_id(),
					'date_created' => $order->get_date_created( 'edit' )->date( TimeInterval::$sql_datetime_format ),
					'tax_rate_id'  => $tax_item->get_rate_id(),
					'shipping_tax' => $tax_item->get_shipping_tax_total(),
					'order_tax'    => $tax_item->get_tax_total(),
					'total_tax'    => (float) $tax_item->get_tax_total() + (float) $tax_item->get_shipping_tax_total(),
				),
				array(
					'%d',
					'%s',
					'%d',
					'%f',
					'%f',
					'%f',
				)
			);

			/**
			 * Fires when tax's reports are updated.
			 *
			 * @param int $tax_rate_id Tax Rate ID.
			 * @param int $order_id    Order ID.
			 */
			do_action( 'woocommerce_analytics_update_tax', $tax_item->get_rate_id(), $order->get_id() );

			// Sum the rows affected. Using REPLACE can affect 2 rows if the row already exists.
			$num_updated += 2 === intval( $result ) ? 1 : intval( $result );
		}

		return ( count( $tax_items ) === $num_updated );
	}

	/**
	 * Clean taxes data when an order is deleted.
	 *
	 * @param int $order_id Order ID.
	 */
	public static function sync_on_order_delete( $order_id ) {
		global $wpdb;

		$wpdb->delete( self::get_db_table_name(), array( 'order_id' => $order_id ) );

		/**
		 * Fires when tax's reports are removed from database.
		 *
		 * @param int $tax_rate_id Tax Rate ID.
		 * @param int $order_id    Order ID.
		 */
		do_action( 'woocommerce_analytics_delete_tax', 0, $order_id );

		ReportsCache::invalidate();
	}

	/**
	 * Initialize query objects.
	 */
	protected function initialize_queries() {
		$this->clear_all_clauses();
		$this->subquery = new SqlQuery( $this->context . '_subquery' );
		$this->subquery->add_sql_clause( 'select', self::get_db_table_name() . '.tax_rate_id' );
		$this->subquery->add_sql_clause( 'from', self::get_db_table_name() );
		$this->subquery->add_sql_clause( 'group_by', self::get_db_table_name() . '.tax_rate_id' );
	}
}