if for migration

db/migrate/20121218164840_move_noteable_commit_to_own_field.rb

@@ -3,7 +3,13 @@ class MoveNoteableCommitToOwnField < ActiveRecord::Migration
     add_column :notes, :commit_id, :string, null: true
     add_column :notes, :new_noteable_id, :integer, null: true
     Note.where(noteable_type: 'Commit').update_all('commit_id = noteable_id')
-    Note.where("noteable_type != 'Commit'").update_all('new_noteable_id = CAST (noteable_id AS INTEGER)')
+
+    if ActiveRecord::Base.connection.adapter_name == 'PostgreSQL'
+      Note.where("noteable_type != 'Commit'").update_all('new_noteable_id = CAST (noteable_id AS INTEGER)')
+    else
+      Note.where("noteable_type != 'Commit'").update_all('new_noteable_id = noteable_id')
+    end
+
     remove_column :notes, :noteable_id
     rename_column :notes, :new_noteable_id, :noteable_id
   end