1、查询年龄为20,21,22,23岁的员工信息

select * from emp where age in(20, 21, 22, 23) and gender = '女';

2、查询性别为男，并且年龄在20-40岁（含）以内的姓名为三个字的员工

select * from emp where gender = '男' && age between 20 and 40 && name like '___';

3、统计员工表中，年龄小于60岁的，男性员工和女性员工的人数

select gender, count(*) from emp where age < 60 group by gender;

4、查询所有年龄小于等于35岁员工的姓名和年龄，并对查询结果按年龄升序排序，如果年龄相同按入职时间降序排序

select name, age, entrydate from emp where age <=35 order by age, entrydate desc;

5、查询性别为男，且年龄在20-40岁（含）以内的前5个员工信息，对查询的结果按年龄升序排序，年龄相同按入职时间升序排序

select * from emp where gender = '男' && age between 20 and 40 order by age, entrydate desc limit 5;