DEV: correct drop logic for columns in post table

We need to recreate the badge_posts view each time we change
column on the posts table.

The p.* is auto expanded on view create, cascade should not have
been used

db/post_migrate/20200430010528_remove_avg_time_from_topics_posts.rb

@@ -6,12 +6,33 @@ class RemoveAvgTimeFromTopicsPosts < ActiveRecord::Migration[6.0]
   def up
     # this makes it re-runnable and also works if it was not created initially
     execute <<~SQL
-      ALTER TABLE topics DROP COLUMN IF EXISTS avg_time CASCADE
+      ALTER TABLE topics DROP COLUMN IF EXISTS avg_time
     SQL
 
-    execute <<~SQL
-      ALTER TABLE posts DROP COLUMN IF EXISTS avg_time CASCADE
-    SQL
+    ActiveRecord::Base.transaction do
+      execute "DROP VIEW badge_posts"
+
+      execute <<~SQL
+        ALTER TABLE posts DROP COLUMN IF EXISTS avg_time
+      SQL
+
+      # we must recreate this view every time we amend posts
+      # p.* is auto expanded and persisted into the view definition
+      # at create time
+      execute <<~SQL
+        CREATE VIEW badge_posts AS
+        SELECT p.*
+        FROM posts p
+        JOIN topics t ON t.id = p.topic_id
+        JOIN categories c ON c.id = t.category_id
+        WHERE c.allow_badges AND
+              p.deleted_at IS NULL AND
+              t.deleted_at IS NULL AND
+              NOT c.read_restricted AND
+              t.visible AND
+              p.post_type IN (1,2,3)
+      SQL
+    end
   end
 
   def down