SQL 查询未选修'020101A'课程的学生学号 (三种方法)

方法一：

SELECT student_id FROM student_course
WHERE course_id <> '020101A'
GROUP BY student_id;

方法二：

SELECT student_id FROM student
WHERE student_id NOT IN (
    SELECT student_id FROM student_course
    WHERE course_id = '020101A'
);

方法三：

SELECT DISTINCT student_id FROM student_course sc1
WHERE NOT EXISTS (
    SELECT * FROM student_course sc2
    WHERE sc1.student_id = sc2.student_id
    AND course_id = '020101A'
);