1、数值比较
运算符
> >=
< <=
= !=
实例
'1.查询成绩及格的学生'
select * from students where score > 60;
'2.删除成绩不及格的学生'
delete from students where score < 60;
'3.把id为3的学生的姓名改为 周芷若'
update students set name='周芷若' where id=3;
2、逻辑比较
运算符
and
or
实例
'查询成绩不及格 或 是男生的学生'
select * from students where score <60 or gender='male';
'查询成绩在60-70之间的学生'
select * from students where score >=60 and score <= 70;
3、范围内
运算符
between value1 and value2
in()
not in()
实例
'查询不及格的学生姓名及成绩'
select name, score from students where score between 0 and 59;
'查询AID19和AID18班的学生姓名及成绩'
select name,score from students where class in('AID19', 'AID18');
4、模糊比较
运算符
where 字段名 like 表达式(%_)
实例
'查询姓赵的学生信息'
select * from students where name like '赵%'
5、NULL判断
运算符
is NULL
is not NULL
实例
'查询姓名字段值为NULL的学生信息'
select * from students where name is NULL;
查询 order by 和 limit
order by 排序
格式
order by 字段名 ASC/DESC 升序/降序
实例
'查询成绩从高到低排列'
select * from students order by score DESC;
limit 输出个数
格式
limit n 显示前n条
limit m, n 从第(m+1)条记录开始,显示n条
'查询成绩从高到低排列 前三名'
select * from students order by score DESC limit 3;