在2018年的mysql實訓中，學生需要完成一個題目，答案如下：

-- 1. 查詢每個部門請假天數大于等于3天的學生姓名和請假天數
SELECT sname, leavedays
FROM student JOIN department ON student.dno = department.dno
WHERE leavedays >= 3;
-- 2. 查詢所有選修了“計算機基礎”課程且成績為80分以上的學生信息
SELECT *
FROM student JOIN sc ON student.sno = sc.sno
WHERE sc.cno = (SELECT cno FROM course WHERE cname = '計算機基礎') AND score >= 80;
-- 3. 查詢所有2018年入學的學生及其所在系別
SELECT sname, dname
FROM student JOIN department ON student.dno = department.dno
WHERE in_year = 2018;
-- 4. 查詢學生所選課程超過4門的學生學號和姓名
SELECT sno, sname
FROM student JOIN (SELECT sno, COUNT(*) AS course_num FROM sc GROUP BY sno) temp ON student.sno = temp.sno
WHERE course_num >4;
-- 5. 查詢選課人數最多的前兩門課程的課程名和選課人數
SELECT cname, COUNT(*) AS num
FROM course JOIN sc ON course.cno = sc.cno
GROUP BY sc.cno
ORDER BY num DESC
LIMIT 2;

這些答案可以作為mysql實訓的參考，也可供其他mysql學習者參考。