SQL两个表查询
select tname from teacher where tno IN(select x.tno from course x,score y where x.cno=y.cno group by x.tno having count(x.tno)>5);
这条查询语句中的select x.tno from course x,score y where x.cno=y.cno group by x.tno having count(x.tno)>5不太明白，这是什么语法？
x.cno=y.cno不应该是内连接的方式吗，这里为什么没有join语句？
