add uniqueness constraint on user names

db/migrate/20170414005856_add_unique_name_constraint_to_users.rb

@@ -0,0 +1,6 @@
+class AddUniqueNameConstraintToUsers < ActiveRecord::Migration
+  def up
+  	remove_index :users, :name
+  	execute "create unique index index_users_on_name on users(lower(name))"
+  end
+end

db/structure.sql

@@ -7579,3 +7579,5 @@ INSERT INTO schema_migrations (version) VALUES ('20170330230231');
 
 INSERT INTO schema_migrations (version) VALUES ('20170413000209');
 
+INSERT INTO schema_migrations (version) VALUES ('20170414005856');
+

script/fixes/045_dedup_users.rb

@@ -0,0 +1,15 @@
+#!/usr/bin/env ruby
+
+require File.expand_path(File.join(File.dirname(__FILE__), '..', '..', 'config', 'environment'))
+
+ActiveRecord::Base.connection.execute("set statement_timeout = 0")
+
+candidates = User.group("lower(name)").having("count(*) > 1").pluck("lower(name)")
+
+candidates.each do |name|
+  users = User.where("lower(name) = ?", name).order("id").to_a
+  users.slice(1, 100).each do |user|
+    user.name = "dup_#{user.name}_#{user.id}"
+    user.save!
+  end
+end