Oracle SQL减去帮助:展示教师教授特定而不有资格教特定课程的教师

Question

1st表

CREATE TABLE qualified (
    facultyid integer NOT NULL,
    courseid character varying(16) NOT NULL,
    datequalified character varying(16),
    dq2 date,
    CONSTRAINT qualified_pkey PRIMARY KEY (facultyid, courseid)
);
INSERT INTO qualified VALUES (3467, 'ISM 4212', to_date('9/1995', 'MM/YYYY'), date '1995-09-01');
INSERT INTO qualified VALUES (4756, 'ISM 3112', to_date('9/1991', 'MM/YYYY'), date '1991-09-01');
INSERT INTO qualified VALUES (2143, 'ISM 3113', to_date('9/1988', 'MM/YYYY'), date '1988-09-01');
INSERT INTO qualified VALUES (4756, 'ISM 3113', to_date('9/1991', 'MM/YYYY'), date '1991-09-01');
INSERT INTO qualified VALUES (2143, 'ISM 3112', to_date('9/1988', 'MM/YYYY'), date '1988-09-01');
INSERT INTO qualified VALUES (3467, 'ISM 4930', to_date('9/1996', 'MM/YYYY'), date '1996-09-01');

第二个表：

CREATE TABLE faculty (
    facultyid integer NOT NULL,
    facultyname character varying(25),
    CONSTRAINT faculty_pkey PRIMARY KEY (facultyid)
);
INSERT INTO faculty VALUES (2143, 'Birkin');
INSERT INTO faculty VALUES (3467, 'Berndt');
INSERT INTO faculty VALUES (4756, 'Collins');

查询：是否有任何讲师有资格教ISM 4212，并且没有资格教ISM 4930？

我尝试的查询：

SELECT q.facultyid, facultyname, q.courseid
FROM qualified q, faculty fa
WHERE q.facultyid = fa.facultyid AND courseid = 'ISM 4212'
MINUS
SELECT q.facultyid, facultyname, q.courseid
FROM qualified q, faculty fa
WHERE q.facultyid = fa.facultyid AND courseid = 'ISM 4930';

显示：3467 berndt ism 4212

而不是：没有/没有结果。

Answer 1

从选择子句中删除以下内容解决了问题：

q.courseid