-- 已有库增量：包裹明细增加属性字段 AttributeText
-- 可重复执行

SET @col_exists := (
  SELECT COUNT(1)
  FROM information_schema.COLUMNS
  WHERE TABLE_SCHEMA = DATABASE()
    AND TABLE_NAME = 'C_parcel_item'
    AND COLUMN_NAME = 'AttributeText'
);

SET @sql := IF(
  @col_exists = 0,
  'ALTER TABLE `C_parcel_item` ADD COLUMN `AttributeText` VARCHAR(256) NULL COMMENT ''规格属性'' AFTER `ProductName`',
  'SELECT ''C_parcel_item.AttributeText already exists'' AS info'
);

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;