1、只查询ID为2,4,6的信息
select username from user where id in (2,4,6);
2、除了不查询ID为2,4,6的信息外，其他的信息
select username from user where not id in (2,4,6);
3、查询sex中开头为w的信息
select username,age from user where sex like 'w%';
4、查询address中中间有u的信息,'_'的使用
select username,age from user where address like '_u%';
查询address中含有a的信息
select username,age from user where address like '%a%';
5、按年龄排序
select*from user order by age asc;(升序)
select*from user order by age desc;(j降序)
6、limit的使用
限制查询前5个信息
