1.select first 1 * from shop; 正序查询第一条数据
2.select first 1 * from shop order by create_time desc; 按创建时间倒序查询第一条数据
3.select first 1 shopid from shop; 正序查询第一条数据中的shopid字段
4.select first 1 shopid from shop order by create_time desc; 按创建时间倒序查询第一条数据的shopid字段