MySQL面試試題與答案

本次試題設計兩個表：student、exam

           student表

          exam表

 

1、寫一條SQL語句，按學號排序輸出數學成績

SELECT s.sno sno,score
FROM exam e,student s
WHERE e.`subject` = '數學' AND e.name = s.name
GROUP BY s.sno

 

2、寫一條SQL語句，按學號排序，輸出：學號，姓名，總分，平均分

SELECT sno,s.`name`,SUM(score) ss,AVG(score) gg
FROM exam e,student s
WHERE e.`name` = s.`name`
GROUP BY `name`
ORDER BY ss

 

3、寫一條SQL語句，查詢出數學考試成績最高的學生學號和姓名

SELECT sno,exam.name name,score
FROM exam,student
WHERE (exam.`subject` = '數學') AND (exam.name = student.name)
ORDER BY exam.score DESC
LIMIT 0,1;

 

4、寫一條SQL語句，查詢出每門課都大於80分的學生姓名

方法一：ALL()函數

思路：查找出每一個人全部科目是否都大於80

SELECT DISTINCT NAME 
FROM exam a
WHERE 80 < ALL(SELECT score 
               FROM exam e
               WHERE e.name = a.name );

 

方法二：not exists 字段

思路：排除掉存在學科分數低於80的學生，剩下的就是全部學科分數都大於80的學生

SELECT DISTINCT NAME
FROM exam a
WHERE NOT EXISTS (SELECT name
                  FROM exam e 
                  WHERE e.name = a.name AND e.score < 80 );

 

方法三：not in 字段

思路：同上

SELECT DISTINCT NAME 
FROM exam 
WHERE NAME NOT IN (SELECT  NAME 
                   FROM exam
                   WHERE score<=80)

 

方法四：having 字段

思路：過濾出學科中最低分數大於80的學生

SELECT name
FROM exam
GROUP BY name
HAVING min(score) > 80

 

5、張三退學後，請寫相關的SQL語句，注意嚴謹

DELETE
FROM exam
WHERE name = '張三';
DELETE
FROM student
WHERE name = '張三';

 

DELETE exam,student
FROM exam
LEFT JOIN student
ON exam.name = student.name
WHERE exam.name = '張三' ;

 

6、你會對該表哪些字段作索引

id - 惟一索引

7、這兩個表的設計，有哪些能夠改進的地方

student表中sno字段能夠改爲‘studentID’，更語義化，

exam表中取消name字段及該列數據，改用student中sno學號字段代替，更易於檢索