sql語句的聯(lián)合查詢(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 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?
結(jié)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?
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 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?
結(jié)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?
?
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