ALTER TABLE `user_simulation_stats`
DROP COLUMN `map_prd_id`,
MODIFY COLUMN `role`  varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '用户角色' AFTER `prd_type`,
MODIFY COLUMN `end_time`  datetime NOT NULL DEFAULT now() ON UPDATE CURRENT_TIMESTAMP COMMENT '结束时间' AFTER `role`,
MODIFY COLUMN `duration`  int(11) NOT NULL COMMENT '有效时长' AFTER `end_time`,
ADD COLUMN `start_time`  datetime NOT NULL DEFAULT now() ON UPDATE CURRENT_TIMESTAMP COMMENT '开始时间' AFTER `role`;
