text: --*************************GO-LICENSE-START*********************************
  -- Copyright 2014 ThoughtWorks, Inc.
  --
  -- Licensed under the Apache License, Version 2.0 (the "License");
  -- you may not use this file except in compliance with the License.
  -- You may obtain a copy of the License at
  --
  --    http://www.apache.org/licenses/LICENSE-2.0
  --
  -- Unless required by applicable law or agreed to in writing, software
  -- distributed under the License is distributed on an "AS IS" BASIS,
  -- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  -- See the License for the specific language governing permissions and
  -- limitations under the License.
  --*************************GO-LICENSE-END***********************************
  
  
  ALTER TABLE users ADD COLUMN preffered_id BIGINT;
  ALTER TABLE users ADD COLUMN in_name varchar_ignorecase(255);
  UPDATE users SET in_name = name;
  
  CREATE TABLE preffered AS SELECT MIN(id) id, in_name FROM users WHERE enabled = true GROUP BY in_name;
  UPDATE users SET preffered_id = (SELECT preffered.id FROM preffered WHERE users.in_name = preffered.in_name);
  DELETE FROM users WHERE preffered_id IS NOT NULL AND id != preffered_id;
  
  DROP TABLE preffered;
  CREATE TABLE preffered AS SELECT MIN(id) id, in_name FROM users WHERE preffered_id IS NULL GROUP BY in_name;
  UPDATE users SET preffered_id = (SELECT preffered.id FROM preffered WHERE users.in_name = preffered.in_name) WHERE preffered_id IS NULL;
  DELETE FROM users WHERE id != preffered_id;
  
  ALTER TABLE users DROP COLUMN preffered_id;
  ALTER TABLE users DROP COLUMN in_name;
  
  ALTER TABLE users ALTER COLUMN name varchar_ignorecase(255) NOT NULL;
  
  --//@UNDO
  
  ALTER TABLE users ALTER COLUMN name VARCHAR(255) NOT NULL;
  