ALTER TABLE `tasks` ADD COLUMN `related_task_id` VARCHAR(64) NOT NULL DEFAULT '' AFTER `join_qr_code`;
-- statement-breakpoint
ALTER TABLE `contents` ADD COLUMN `related_content_id` VARCHAR(64) NOT NULL DEFAULT '' AFTER `source_row`;
-- statement-breakpoint
CREATE INDEX `contents_related_content_idx` ON `contents` (`related_content_id`);