-- 附加费增加可计算条件。已有库可重复执行。
SET NAMES utf8mb4;

SET @sql = (
  SELECT IF(
    COUNT(*) = 0,
    'ALTER TABLE pay_surcharge
       ADD COLUMN calc_rule varchar(20) NOT NULL DEFAULT ''MANUAL'' COMMENT ''计费条件：ALWAYS每票、POSTCODE邮编、WEIGHT超重、SIZE超尺寸、RETURN退件、MANUAL人工'' AFTER charge_timing,
       ADD COLUMN calc_param varchar(1000) DEFAULT NULL COMMENT ''条件参数，如邮编、重量阈值、尺寸表达式'' AFTER calc_rule',
    'SELECT 1'
  )
  FROM information_schema.COLUMNS
  WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = 'pay_surcharge' AND COLUMN_NAME = 'calc_rule'
);
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;