code refactor

sql/n9e.sql

@@ -309,7 +309,7 @@ CREATE TABLE `alert_event` (
     `notify_users` varchar(255) not null default '',
     `runbook_url` varchar(255),
     `readable_expression` varchar(1024) not null comment 'e.g. mem.bytes.used.percent(all,60s) > 0',
-    `tags` varchar(1024) not null default 'merge data_tags rule_tags and res_tags',
+    `tags` varchar(1024) not null default '' comment 'merge data_tags rule_tags and res_tags',
     PRIMARY KEY (`id`),
     KEY (`hash_id`),
     KEY (`rule_id`),
@@ -336,7 +336,7 @@ CREATE TABLE `history_alert_event` (
   `notify_users` varchar(255) not null default '',
   `runbook_url` varchar(255) default NULL,
   `readable_expression` varchar(1024) not null COMMENT 'e.g. mem.bytes.used.percent(all,60s) > 0',
-  `tags` varchar(1024) not null default 'merge data_tags rule_tags and res_tags',
+  `tags` varchar(1024) not null default '' COMMENT 'merge data_tags rule_tags and res_tags',
   PRIMARY KEY (`id`),
   KEY `hash_id` (`hash_id`),
   KEY `rule_id` (`rule_id`),