Sql语句关外连接查询

外连接
 [例]外连接实例
create table students
   (
          st_id    varchar(20),
          name  varchar(10),
          age      int,
          tol_score  int
    );

    insert into students values('973231','wangbindu',22,501);
    insert into students values('973232','zhuzhijing',21,538);
    insert into students values('973233','gaojing',21,576);

  create table student_skill
   (
      st_id  varchar(20),
      skill    varchar(20)
   );

    insert into student_skill values('973231','篮球');
    insert into student_skill(st_id) values('973232');
    insert into student_skill values('973233','足球');

   select a.* , b.skill from students a,student_skill b where a.st_id=b.st_id
order by a.st_id;

select students.st_id , students.name , students.age , students.tol_score , student_skill.skill from
students,student_skill where students.st_id=student_skill.st_id;