增：
INSERT INTO `tian` (`id`,`num`) values (null,'" + (addNum + 1) + "');
删：
//快速删除表，返回0
truncate table 表名
//返回被删除的记录数
DELETE FROM 表名
DELETE FROM `表名 ` WHERE `id` = 1 ;
改：
update `tian` set name="天域苍穹" WHERE `id`>=0 ;
查：
"SELECT num FROM `表名` ORDER BY id DESC LIMIT 1 OFFSET 1 "
//SELECT num FROM `表名` , 查询tian表中num
//ORDER BY id DESC , 按id倒序排序
//LIMIT 1 查询一条
//OFFSET 1 偏移量，就是跳过多少个
