sql语句的联合查询(join 用法)

sql语句的联合查询(join 用法)
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‚