TreeMap 升序|降序排列 import java.util.Comparator; import java.util.TreeMap; public class Main { public static void main(String[] args) { TreeMap<Integer,Integer> map1 = new TreeMap<Integer,Integer>(); //默认的TreeMap升序排列 TreeMap<Integer,Integer>
select *from wsb limit 5;显示前5行 select *from students LIMIT (m,n) (其中m是指记录开始的index,从0开始,表示第一条记录n是指从第m+1条开始,取n条.select * from tablename limit 2,4即取出第3条至第6条,4条记录) +where 筛选条件 select *from wsb where salary>2000; select *from where age is null;(空字段