-- =============================================================================
-- 运输管理 · 车辆表增加挂车号
-- 执行库：shanxia2.0 门户库（与 web-admin 同库）
-- 说明：可重复执行；挂车号为车辆主数据属性，地磅/出入库仍使用 license_plate
-- =============================================================================

SET NAMES utf8mb4;

SET @col_exists := (
  SELECT COUNT(*)
  FROM information_schema.COLUMNS
  WHERE TABLE_SCHEMA = DATABASE()
    AND TABLE_NAME = 'pl_vehicle'
    AND COLUMN_NAME = 'trailer_no'
);

SET @ddl := IF(
  @col_exists = 0,
  'ALTER TABLE `pl_vehicle` ADD COLUMN `trailer_no` varchar(20) DEFAULT NULL COMMENT ''挂车号'' AFTER `license_plate`',
  'SELECT ''trailer_no already exists'' AS message'
);

PREPARE stmt FROM @ddl;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

SELECT COLUMN_NAME, COLUMN_TYPE, IS_NULLABLE, COLUMN_COMMENT
FROM information_schema.COLUMNS
WHERE TABLE_SCHEMA = DATABASE()
  AND TABLE_NAME = 'pl_vehicle'
  AND COLUMN_NAME IN ('license_plate', 'trailer_no')
ORDER BY ORDINAL_POSITION;