select * from student s Join class c on s.class_id = c.id
select * from student s left join class c on s.class_id = c.id
select * from student s right join class c on s.class_id = c.id
select * from student s Join class c on s.class_id = c.id
select * from student s left join class c on s.class_id = c.id
select * from student s right join class c on s.class_id = c.id
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