SET @column_exists := (
    SELECT COUNT(1)
    FROM information_schema.COLUMNS
    WHERE TABLE_SCHEMA = DATABASE()
      AND TABLE_NAME = 't_parking_lot'
      AND COLUMN_NAME = 'barrier_brand'
);

SET @ddl := IF(
    @column_exists = 0,
    'ALTER TABLE `t_parking_lot` ADD COLUMN `barrier_brand` int NULL DEFAULT NULL COMMENT ''道闸品牌：1舜杰，2捷联'' AFTER `type`',
    'SELECT 1'
);

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

UPDATE `t_parking_lot`
SET `barrier_brand` = 2
WHERE `barrier_brand` IS NULL;