MySQL内联，左联，右联

有两张表student表和teacher表
学生表：

老师表：

1.左联
select student.user_name,student.age,student.class_id,teacher.t_name from student left join teacher on student.class_id = teacher.class_id;
查询结果：返回左边表所有被查询字段的信息+右边表中符合条件的字段

2.右联
select teacher.work_id,teacher.t_name,teacher.class_id,student.user_name from teacher right join student on teacher.class_id = student.class_id;
查询结果：返回右边表所有被查询字段的信息+左边表中符合条件的字段

3.内联
select student.user_name,student.age,student.class_id,teacher.t_name from student inner join teacher on student.class_id = teacher.class_id;
查询结果：只返回符合条件的字段的信息