ALTER TABLE `debtors_detail`
  ADD `credit_limit_changed_at` DATETIME NULL
  AFTER `credit_limit`,
  ADD `credit_limit_changed_by` TINYINT(3) NULL
  AFTER `credit_limit_changed_at`,
  ADD `credit_limit_old_value` INT(11) NULL
  AFTER `credit_limit_changed_by`;
ALTER TABLE `debtors_detail`
  ADD `trade_limit_changed_at` DATETIME NULL
  AFTER `trade_limit`,
  ADD `trade_limit_changed_by` TINYINT(3) NULL
  AFTER `trade_limit_changed_at`,
  ADD `trade_limit_old_value` INT(11) NULL
  AFTER `trade_limit_changed_by`;
ALTER TABLE `debtors_detail`
  ADD `isl_changed_at` DATETIME NULL
  AFTER `insurance_specified_limit`,
  ADD `isl_changed_by` TINYINT(3) NULL
  AFTER `isl_changed_at`,
  ADD `isl_old_value` INT(11) NULL
  AFTER `isl_changed_by`;
ALTER TABLE `debtors_detail`
  ADD `cr_changed_at` DATETIME NULL
  AFTER `credit_risk`,
  ADD `cr_changed_by` TINYINT(3) NULL
  AFTER `cr_changed_at`,
  ADD `cr_old_value` INT(11) NULL
  AFTER `cr_changed_by`;