this->table_name} ADD COLUMN job_id VARCHAR(255) NULL default '' AFTER is_mobile " );
		}
		if ( ! $queuename_column_exists ) {
			$created &= $this->get_db()->query( "ALTER TABLE {$this->table_name} ADD COLUMN queue_name VARCHAR(255) NULL default '' AFTER job_id " );
		}
		if ( ! $status_column_exists ) {
			$created &= $this->get_db()->query( "ALTER TABLE {$this->table_name} ADD COLUMN status VARCHAR(255) NULL default '' AFTER queue_name " );
		}

		return $this->is_success( $created );
	}

	/**
	 * Make status column as index.
	 *
	 * @return bool
	 */
	protected function make_status_column_index() {
		$queuename_column_exists = $this->column_exists( 'queue_name' );
		if ( ! $queuename_column_exists ) {
			return $this->is_success( false );
		}

		if ( $this->index_exists( 'queue_name_index' ) ) {
			return $this->is_success( true );
		}

		$index_added = $this->get_db()->query( "ALTER TABLE {$this->table_name} ADD INDEX `queue_name_index` (`queue_name`) " );
		return $this->is_success( $index_added );
	}

	/**
	 * Add hash column and index
	 *
	 * @return bool
	 */
	protected function add_hash_column() {
		$hash_column_exists = $this->column_exists( 'hash' );

		$created = true;

		if ( ! $hash_column_exists ) {
			$created &= $this->get_db()->query( "ALTER TABLE {$this->table_name} ADD COLUMN hash VARCHAR(32) NULL default '' AFTER css, ADD KEY hash (hash) " );
		}

		return $this->is_success( $created );
	}

	/**
	 * Make status column as index.
	 *
	 * @return bool
	 */
	protected function make_status_column_index_instead_queue_name() {
		$queuename_column_exists = $this->column_exists( 'status' );
		if ( ! $queuename_column_exists ) {
			return $this->is_success( false );
		}

		if ( $this->index_exists( 'status_index' ) ) {
			return $this->is_success( true );
		}

		if ( $this->index_exists( 'queue_name_index' ) ) {
			if ( ! $this->get_db()->query( "ALTER TABLE {$this->table_name} DROP INDEX `queue_name_index`" ) ) {
				return $this->is_success( false );
			}
		}

		$index_added = $this->get_db()->query( "ALTER TABLE {$this->table_name} ADD INDEX `status_index` (`status`(191)) " );

		return $this->is_success( $index_added );
	}

	/**
	 * Remove all completed rows.
	 *
	 * @return bool|int
	 */
	public function remove_all_completed_rows() {
		// Get the database interface.
		$db = $this->get_db();

		// Bail if no database interface is available.
		if ( empty( $db ) ) {
			return false;
		}

		$prefixed_table_name = $this->apply_prefix( $this->table_name );
		return $db->query( "DELETE FROM `$prefixed_table_name` WHERE status IN ( 'failed', 'completed' )" );
	}

	/**
	 * Returns name from table.
	 *
	 * @return string
	 */
	public function get_name() {
		return $this->apply_prefix( $this->table_name );
	}

	/**
	 * Trigger recreation of cache table if not exist.
	 *
	 * @return void
	 */
	public function maybe_trigger_recreate_table() {
		if ( $this->exists() ) {
			return;
		}

		delete_option( $this->db_version_key );
	}

	/**
	 * Add error columns
	 *
	 * @return bool
	 */
	protected function add_error_columns() {
		return $this->add_error_message_column() && $this->add_error_code_column() && $this->make_error_code_column_index();
	}

	/**
	 * Add error_message column and index
	 *
	 * @return bool
	 */
	private function add_error_message_column() {
		$error_message_column_exists = $this->column_exists( 'error_message' );

		$created = true;

		if ( ! $error_message_column_exists ) {
			$created &= $this->get_db()->query( "ALTER TABLE `{$this->table_name}` ADD COLUMN error_message longtext NULL default NULL AFTER hash" );
		}

		return $this->is_success( $created );
	}

	/**
	 * Add error_code column and index
	 *
	 * @return bool
	 */
	private function add_error_code_column() {
		$error_code_column_exists = $this->column_exists( 'error_code' );

		$created = true;

		if ( ! $error_code_column_exists ) {
			$created &= $this->get_db()->query( "ALTER TABLE `{$this->table_name}` ADD COLUMN error_code VARCHAR(32) NULL default NULL AFTER hash" );
		}

		return $this->is_success( $created );
	}

	/**
	 * Make status column as index.
	 *
	 * @return bool
	 */
	private function make_error_code_column_index() {
		$error_code_column_exists = $this->column_exists( 'error_code' );
		if ( ! $error_code_column_exists ) {
			return $this->is_success( false );
		}

		if ( $this->index_exists( 'error_code_index' ) ) {
			return $this->is_success( true );
		}

		$index_added = $this->get_db()->query( "ALTER TABLE {$this->table_name} ADD INDEX `error_code_index` (`error_code`) " );
		return $this->is_success( $index_added );
	}
}