SQL group by,between and,union,having

1、学生表studentCREATETABLE`student`(`id`int(50)NOTNULLAUTO_INCREMENT,`name际吨孔鳝`varchar(50)DEFAULTNULL,`sex`varchar(48)DEFAULTNULL,`age`varchar(50)DEFAULTNULL,`birthday`varchar(50)DEFAULTNULL,PRIMARYKEY(`id`))ENGINE=InnoDBAUTO_INCREMENT=245DEFAULTCHARSET=utf8

3、分组(学生表分组通过班级,查看每班要多少个人）Group bySELECT s.class,COUNT(*) FROM student s GROUP BY s.class

4、外连接（学生表和课程表，找到2个表直接id一样的学生）SELECT * FROM student s,kecheng k WHERE s.id=k.id