小编Man*_*hra的帖子

select deptno  
from emp2  
MINUS  
select deptno 
from dpt  
order by deptno;  

上面的查询返回=没有找到数据

然而,

select deptno,ename   
from emp2  
MINUS  
select deptno,dname 
from dpt   
order by deptno;  

返回所有deptno和ename字段值.

虽然在第二个查询中使用了MINUS运算符,但你能解释为什么我得到了deptno字段的所有值吗？

legend: 
emp is employee table and dpt is department table,
ename is employee name -belonging to emp,
dname is department name -belonging to dpt,
deptno is department no. -common to both