SQL 增删改查

--修改数据库名字 sp_renamedb   数据库名字, 修改后的数据库名字;

--修改 Update     排除  Except      删除表 drop table      删除表数据 delete

--不等于 <>     在里面 in      并且 and    或者 or    在两者之间 between      去除了重复的 distinct

--from 谁，谁就是左表  inner join：内联接   left join  左外连接    right join 右外连接

--SQL 查询举例 ：

--简单的多表联合查询，选了课的学生和他选的课

select s.*, cName,cGrade from sc inner join student s on s.stuId = sc.stuId

--求平均成绩最大的系和系的人数与它的平均成绩(2种方法)

select top 1 stuDept, count(*) as 人数, avg(stuAvgrade) from student

group by stuDept order by avgrade desc

select stuDept, count(*) as 人数, avg(stuAvgrade) from student

group by stuDept having avg(stuAvgrade) =

(select top 1 avg(stuAvgrade) as allAvg from student group by stuDept order by allAvg desc)

查某某同学跟了哪几个老师

select * from teacher
where tId in
(
    select tId from teacherStudentDetail
    where stuId = (select stuId from student where stuName = '某某')
)