一、范围查询
（1）查询年纪在18-20岁的学生名字；
select name from students where age=18 or age=19 or age=20;
select name from students where age in (18,19,20);
select name from students where age between 18 and 20;
--不在18-20岁之间的；
select name from students where age not in (18,19,29);
select name from students where age not between 18 and 20; ---注意不能写成 not (between 18 and 20);
（2）查询年纪为空的学生名字；
select name from students where age is null；----不为空：is not null
（3）查询名字有两个字的；
select name from students where name like '__'（两个下划线）
（4）查询名字以“周”开始的；
select name from students where name like‘周%’；
select name from students where name rlike '^周.*';
（5）查询名字以“周”开始，以“伦”结尾的；
select name from students where name like ‘周%伦’；
select name from students where name rlike '^周.*伦$'；
（6）查询名字至少有两个字的；
select name from students where name like‘__%’;
select name from students where name rlike 'dd*';
二、排序
（1）按年纪从小到大排序；
select * from students order by age；（默认是按照从小到大）
select * from students order by age asc；
（2）按照年纪从大到小排序
select * from students order by age desc;