對SQL 集合查詢的一些了解【SQL】

設A， B為兩個查詢--

A     union      B      傳回A與B的并集

A    except     B       傳回A中元素且不是B中的元素

A  intersect   B    傳回A與B的交集

可通過以下代碼來做實驗---

select stu_id , name , mark , sdept 
from stu_info 
where sdept ='計算機系';

select stu_id , name , mark , sdept 
from stu_info 
where mark >550;



select stu_id , name , mark , sdept 
from stu_info 
where sdept ='計算機系'
union 
select stu_id , name , mark , sdept 
from stu_info 
where mark >550;



select stu_id , name , mark , sdept 
from stu_info 
where sdept ='計算機系'
except
select stu_id , name , mark , sdept 
from stu_info 
where mark >550;

select stu_id , name , mark , sdept 
from stu_info 
where sdept ='計算機系'
intersect
select stu_id , name , mark , sdept 
from stu_info 
where mark >550;