数据库中关于表的连接问题

 --1内连接（两个表中相匹配的那些记录）
  --2外联接
  --2.1左外联接(把左表中 left join关键字左边的表)中的全部记录都显示出来，对于右表中能找到匹配的记录，显示对应匹配数据，对右表中找不到的匹配记录显示为null。
    --2.2右外联接 left [outter] join,right [outter] join.
    --左外联接和右外联接都是分两步查询出结果的,第一:找到匹配数据,第二:填充不匹配的数据为null。（注意，是有先后顺序的。）
   
    ----Cross Join交叉联接------
    select
      *
    from Student,Score
   
    ----自联接------------------
   
    select
    *
    from Student
    inner join
    (select sName,sAge,sId FROM Student
    where sAge>10
    )as TS1
    ON Student.sId=TS1.sId
   
   -- -7----report 2------
   
   
   
  SELECT
     *
     FROM 
    (select
       sId,
       sName,
       sAge,
       Score.*
    from Student
       left outer join Score
       ON Score.studentId=Student.sId
       ) as Tbl
       WHERE ScoreId is null
 
 ---右外--
 select
       sId,
       sName,
       sAge,
       Score.*
    from Student
       right outer join Score
       ON Score.studentId=Student.sId
 --- ---------------
 select
       sId,
       sName,
       sAge,
       Score.*
    from Score
       right outer join Student
       ON Score.studentId=Student.sId
 
  select
  sId,
  sName,
  Score.*
  FROM Student
  LEFT OUTER JOIN Score
  on Score.studentId=Student.sId
  --重做：查询出所有没有参加考试的同学的学生编号，姓名，考试成绩。
   select
  sId,
  sName,
  Score.*
  FROM Student
  LEFT OUTER JOIN Score
  on Score.studentId=Student.sId
  where Score.scoreId is null
  --2.2右外联接
  select
    Score.*,
    sId,
    sName
    from Student
  right outer join Score on
  Score.scoreId=Student.sId
  ------------
  select
    Score.*,
    sId,
    sName
    from Score
  right outer join Student on
  Score.scoreId=Student.sId
  ----Cross Join 交叉联结-------
  select * from
  Student,Score
  -------自联结------------------
  select *
  from Student
  inner join(select sId,sName,sAge from Student where sAge>=10)as Tbl1
  on Student.sId=Tbl1.sId