SQL Join sentence

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student

no‚name‚classid‚
1‚ zdy‚2‚
2‚huz‚2‚
3‚yxx‚2‚
4‚sss‚1‚

class

classid‚classname‚
2‚y2002‚
3‚y2003‚

1 .select * from student ‚ class where student.classid=class.classid

no‚name‚classid‚classid‚classname‚
1‚zdy‚2‚2‚y2002‚
2‚huz‚2‚2‚y2002‚
3‚yxx‚2‚2‚y2002‚
2.select * from student left join class on student.classid=class.classid

no‚name‚classid‚classid‚classname‚
1‚zdy‚2‚2‚y2002‚
2‚huz‚2‚2‚y2002‚
3‚yxx‚2‚2‚y2002‚
4‚sss‚1‚ ‚ ‚
3.select * from student inner join class on student.classid=class.classid
no‚name‚classid‚classid‚classname‚
1‚zdy‚2‚2‚y2002‚
2‚huz‚2‚2‚y2002‚
3‚yxx‚2‚2‚y2002‚
结果同1

4.select * from student right join class on student.classid=class.classid

no‚name‚classid‚classid‚classname‚
1‚zdy‚2‚2‚y2002‚
2‚huz‚2‚2‚y2002‚
3‚yxx‚2‚2‚y2002‚
‚ ‚ ‚ 3‚y2003‚