基本语句

select *
from student

Where 查询

select *
from student
where Address = '鞍山'

例：在 SC 表中成绩高于 80 分的人

select *
from SC
where chengji > 80

例：查询 ST 表中所有女生的学号和姓名

select STid,STname
from ST
where sex = '女'

例：在 SC 表中成绩在 70-79 分的人

select *
from SC
where chengji >=70 and chengji <= 79

Where not

select *
from SC
where ID not in('001','002')

查询 SC 表中成绩非空且＞90

select *
from SC
where chengji is not null and chengji >= 90

Where like

例：查询所有姓张的学生

select *
from ST
where STname like '张%'

例：查询所有不姓张的学生

select *
from ST
where STname not like '张%'

例：查询所有不姓张且名字是三个汉字的学生

select *
from ST
where STname not like '张__'

between and

例：在 SC 表中成绩在 70-79 分的人

select *
from SC
where between 70 and 79

distinct

distinct 去除重复值

例：查询学生来自哪些城市

select distinct address
from ST

查询有人选修的课程的课程数

select count(distinct SCid)
from SC

count

例：查询城市数量

select count(distinct address)
from ST

AVG（平均值）

例：查询特定课程 id 下的平均值

select AVG(chengji)
from SC
where SCid = '111100'