remove tag duplicates

db/migrate/20150425164647_remove_duplicate_tags.rb

+class RemoveDuplicateTags < ActiveRecord::Migration
+  def up
+    select_all("SELECT name, COUNT(id) as cnt FROM tags GROUP BY name HAVING COUNT(id) > 1").each do |tag|
+      duplicate_ids = select_all("SELECT id FROM tags WHERE name = '#{tag["name"]}'").map{|tag| tag["id"]}
+      origin_tag_id = duplicate_ids.first
+      duplicate_ids.delete origin_tag_id
+
+      execute("UPDATE taggings SET tag_id = #{origin_tag_id} WHERE tag_id IN(#{duplicate_ids.join(",")})")
+      execute("DELETE FROM tags WHERE id IN(#{duplicate_ids.join(",")})")
+    end
+  end
+
+  def down
+    
+  end
+end