FIX: Backfill topic timer duration (#9249)

db/migrate/20200320193612_back_fill_topic_timer_durations.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class BackFillTopicTimerDurations < ActiveRecord::Migration[6.0]
+  def up
+    DB.exec <<~SQL
+      UPDATE topic_timers
+      SET duration = 0
+      WHERE duration IS NULL AND (execute_at IS NULL OR created_at IS NULL)
+    SQL
+
+    DB.exec <<~SQL
+      UPDATE topic_timers
+      SET duration = EXTRACT(EPOCH FROM execute_at - created_at) / 3600
+      WHERE duration IS NULL AND execute_at IS NOT NULL AND created_at IS NOT NULL
+    SQL
+  end
+
+  def down
+  end
+end