交集在 sql 中

Question

我必须在 SQL 的 2 个查询中找到交集并且我正在使用 INTERSECTION 但是当我在命令上尝试它时查询显示没有结果当我知道有一行属于该类别时。 问题如下：查找同时上过 CIS 课程和历史课程的学生的全名这是我的代码：

SELECT student.sid
FROM student
JOIN registration 
ON registration.sid = student.sid
JOIN course 
ON registration.crn = course.crn
WHERE dept= "CIS" 

INTERSECT

SELECT student.sid 
FROM student
JOIN registration 
ON registration.sid = student.sid
JOIN course 
ON registration.crn = course.crn
WHERE dept = "HIS";

Answer 1

这有效

SELECT fName, lName
FROM student
JOIN registration 
ON registration.sid = student.sid
JOIN course 
ON registration.crn = course.crn
WHERE dept= "CIS" 

AND student.sid IN

(SELECT student.sid 
FROM student
JOIN registration 
ON registration.sid = student.sid
JOIN course 
ON registration.crn = course.crn
WHERE dept = "HIS");

Answer 2

尝试EXISTS

SELECT student.sid 
FROM student JOIN registration ON registration.sid = student.sid 
JOIN course ON registration.crn = course.crn WHERE dept= "CIS"
WHERE EXISTS(SELECT student.sid FROM student JOIN registration ON registration.sid = student.sid JOIN course ON registration.crn = course.crn WHERE dept = "HIS");