表连接分为横向表连接和纵向表连接

横向表连接有三种方式：

1、select 列名，列名 from 表名，表名 where 表名.列名=表名.列名

select student.Sno,sname,cno,degree from Student,Score

where Student.Sno = Score.Sno

2、子查询方式

select sno,sname,(select cno from Score where Student.Sno=Score.Sno) from Student

3、select 列名，列名 from 表名 join 表名 on 表名.列名=表名.列名

select Student.Sno,sname,Score.Cno,DEGREE,cname

from Student join Score on Student.Sno=Score.Sno

join Course on Score.Cno = Course.cno

 纵向表连接：（注：两个表必须是同样的列数，对应的列数据类型必须一致）

select  列名，列名 from 表名 union select  列名，列名 from 表名

select sno 编号,sname 姓名,ssex 性别,sbirthday 生日 from Student

union

select tno,tname,tsex,tbirthday from Teacher

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灵活用法

select Student.sno,sname+'同学',cname,abs(degree+10)

from Student,Score,Course

where Student.Sno=Score.Sno and Score.Cno=Course.Cno

and student.Sno='107'