针对一个表简单的查询语句

起别名为c1，c1前面省略了as

select * from student cl

查看前n行

select top 2 * from student

排序:先age降序，再gender升序

select top 2 * from student order by age desc, gender asc

消除重复行,可以查看有多少个分类变量有多少个类别

select distinct gender from student

查询编号为3的性别

select gender from student where id=3

查询age在30-80的

select * from student where age between 30 and 80 --连续的闭区间

查询id为1或者2的

select * from student where id in (1,2) --非连续的数字

--where id=1 or id=2 --返回布尔值

--where id not in (1,2) --取非

查询年纪在20-80的性别为1的

select * from student
where (age between 20 and 80) and (gender='1') --性别设为字符，所以加引号