数据库多表查询--【SQL Server】

连接：join 表名 on 关联条件

内连接：inner join，两表中完全匹配的数据
左外连接：left outer join，两表中完全匹配的数据，左表中特有的数据
右外连接：right outer join，两表中完全匹配的数据，右表中特有的数据
完全外连接：full outer join，两表中完全匹配的数据，左表中特有的数据，右表中特有的数据

select * 
from studentinfo
inner join classinfo on studentinfo.cid=classinfo.cid 

select studentinfo.sname,classinfo.cname
from studentinfo
inner join classinfo on studentinfo.cid=classinfo.cid 

select so.sname,co.cname--建议使用别名
from studentinfo as so
inner join classinfo as co on so.cid=co.cid 

select so.sname,co.cname
from studentinfo as so
right join classinfo as co on so.cid=co.cid 

select so.sname,co.cname
from studentinfo as so
left join classinfo as co on so.cid=co.cid 

select *
from studentinfo as so
full join classinfo as co on so.cid=co.cid 

多表查询：

select st.sname,cl.cname,sc.score,su.sucourse
from sc
inner join  studentinfo as st on sc.cid=st.cid
inner join  subjectinfo as su on sc.sid=su.suid
inner join  classinfo as cl on st.cid=cl.cid