数据库基础SQL知识面试题二
作者：尹正杰
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一.选课系统SQL语法练习
course数据库中有以下四张表： •students表（学生表）： sid整型自增主键，sname字符串64位，gender字符串12位，dept_id整型并外键到dept表的id字段。 •dept表（系表）： id整型自增主键，dept_name字符串64位。 •course表（课程表）： id整型自增字段主键，course_name字符串64位，teacher_id整型外键到teacher表的id字段。 •teacher表（老师表）： id整型自增字段主键，name字符串64位，dept_id整型外键到dept表的id字段。 •score表（选课成绩表）： sid整型自增主键，course_id整型，score整型。 各表的预置数据如下所示： • students表: (1,’Jason Yin’,0,1),(2,’Andy’,0,1),(3,’Bob’,0,1),(4,’Ruth’,1,2),(5,’Mike’,0,2),(6,’John’, 0,3),(7,’Cindy’,1,3),(8,’Susan’,1,3) • dept表: (1,’Education’),(2,’Computer Science’),(3,’Mathematics’) • course表: (1,‘math’,3),(2,’english’,2),(3,’chinese’,4),(4,’history’,1),(5,’biology’,5) • teacher表: (1,’Zhang san’,1),(2,’Li si’,1),(3,’Wang wu’,2),(4,’Liu liu’,3),(5,’Ding qi’,3) • score表: (1,1,76),(1,2,90),(1,3,82),(1,5,56),(2,2,78),(2,4,92),(2,3,77),(2,5,65),(3,1,48),(3, 2,95),(3,3,75),(3,4,89),(3,5,92),(4,3,78),(4,4,67),(5,1,75),(5,3,90),(5,4,82),(6,2,58),(6,4,88),(7,1,55),(7,2,65),(7,3,63),(7,4,68),(7,5,70),(8,4,88),(8,5,100)
1>.请根据上述的信息创建出相应的表和插入预置数据
mysql> CREATE DATABASE course CHARACTER SET = utf8; Query OK, 1 row affected, 1 warning (0.00 sec) mysql> mysql> USE course; Database changed mysql> mysql> SELECT DATABASE(); +------------+ | DATABASE() | +------------+ | course | +------------+ row in set (0.00 sec) mysql> mysql> CREATE TABLE dept(id INT PRIMARY KEY AUTO_INCREMENT,demt_name VARCHAR(64)); Query OK, 0 rows affected (0.01 sec) mysql> mysql> CREATE TABLE students( -> sid INT PRIMARY KEY AUTO_INCREMENT, -> sname VARCHAR(64), -> gender VARCHAR(12), -> dept_id INT NOT NULL, -> CONSTRAINT student_dept FOREIGN KEY(dept_id) REFERENCES dept(id) -> ); Query OK, 0 rows affected (0.02 sec) mysql> mysql> mysql> CREATE TABLE teacher( -> id INT PRIMARY KEY AUTO_INCREMENT, -> name VARCHAR(64), -> dept_id INT NOT NULL, -> CONSTRAINT teacher_dept FOREIGN KEY(dept_id) REFERENCES dept(id) -> ); Query OK, 0 rows affected (0.01 sec) mysql> mysql> CREATE TABLE course( -> id INT PRIMARY KEY AUTO_INCREMENT, -> course_name VARCHAR(64), -> teacher_id INT, -> CONSTRAINT course_teacher FOREIGN KEY(teacher_id) REFERENCES teacher(id) -> ); Query OK, 0 rows affected (0.01 sec) mysql> mysql> CREATE TABLE score(sid INT,course_id INT,score INT,PRIMARY KEY(sid,course_id)); Query OK, 0 rows affected (0.01 sec) mysql>
mysql> INSERT INTO dept VALUES(1,'Education'),(2,'Computer Science'),(3,'Mathematics'); Query OK, 3 rows affected (0.01 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> mysql> INSERT INTO teacher VALUES(1,'Zhang san',1),(2,'Li si',1),(3,'Wang wu',2),(4,'Liu liu',3),(5,'Ding qi',3); Query OK, 5 rows affected (0.00 sec) Records: 5 Duplicates: 0 Warnings: 0 mysql> mysql> INSERT INTO students VALUES(1,'Jason Yin',0,1),(2,'Andy',0,1),(3,'Bob',0,1),(4,'Ruth',1,2),(5,'Mike',0,2),(6,'John',0,3),(7,'Cindy',1,3),(8,'Susan',1,3); Query OK, 8 rows affected (0.00 sec) Records: 8 Duplicates: 0 Warnings: 0 mysql> mysql> INSERT INTO course VALUES(1,'math',3),(2,'english',2),(3,'chinese',4),(4,'history',1),(5,'biology',5); Query OK, 5 rows affected (0.00 sec) Records: 5 Duplicates: 0 Warnings: 0 mysql> mysql> INSERT INTO score VALUES(1,1,76),(1,2,90),(1,3,82),(1,5,56),(2,2,78),(2,4,92),(2,3,77),(2,5,65),(3,1,48),(3,2,95),(3,3,75),(3,4,89),(3,5,92),(4,3,78),(4,4,67),(5,1,75),(5,3,90),(5,4,82),(6,2,58),(6,4,88),(7,1,55),(7,2,65),(7,3,63),(7,4,68),(7,5,70),(8,4,88),(8,5,100); Query OK, 27 rows affected (0.01 sec) Records: 27 Duplicates: 0 Warnings: 0 mysql> mysql>
2>.查看所有英语成绩超过数学成绩的学生的学号和姓名
mysql> SELECT aa.sid,aa.sname FROM (SELECT a1.sid,sname,score FROM students a1 INNER JOIN score b1 ON a1.sid=b1.sid WHERE course_id=2) aa INNER JOIN (SELECT a2.sid,sname, score FROM students a2 INNER JOIN score b2 ON a2.sid=b2.sid WHERE course_id=1) bb ON aa.sid=bb.sid WHERE aa.score>bb.score; +-----+-----------+ | sid | sname | +-----+-----------+ | 1 | Jason Yin | | 3 | Bob | | 7 | Cindy | +-----+-----------+ 3 rows in set (0.00 sec) mysql> mysql>
3>.查看平均成绩大于等于60的所有学生的姓名和平均成绩
mysql> SELECT a.sid,a.sname,AVG(b.score) FROM students a INNER JOIN score b ON a.sid=b.sid GROUP BY a.sid,a.sname HAVING AVG(b.score)>=60; +-----+-----------+--------------+ | sid | sname | AVG(b.score) | +-----+-----------+--------------+ | 1 | Jason Yin | 76.0000 | | 2 | Andy | 78.0000 | | 3 | Bob | 79.8000 | | 4 | Ruth | 72.5000 | | 5 | Mike | 82.3333 | | 6 | John | 73.0000 | | 7 | Cindy | 64.2000 | | 8 | Susan | 94.0000 | +-----+-----------+--------------+ 8 rows in set (0.00 sec) mysql> mysql>
4>.查询所有同学的学号，姓名，选课数和总成绩
mysql> SELECT a.sid,a.sname,COUNT(*),SUM(score) FROM students a INNER JOIN score b ON a.sid=b.sid GROUP BY a.sid,a.sname; +-----+-----------+----------+------------+ | sid | sname | COUNT(*) | SUM(score) | +-----+-----------+----------+------------+ | 1 | Jason Yin | 4 | 304 | | 2 | Andy | 4 | 312 | | 3 | Bob | 5 | 399 | | 4 | Ruth | 2 | 145 | | 5 | Mike | 3 | 247 | | 6 | John | 2 | 146 | | 7 | Cindy | 5 | 321 | | 8 | Susan | 2 | 188 | +-----+-----------+----------+------------+ 8 rows in set (0.00 sec) mysql> mysql>
5>.查询姓zhang的老师的个数
mysql> SELECT count(*) FROM teacher WHERE name LIKE 'zhang%'; +----------+ | count(*) | +----------+ | 1 | +----------+ 1 row in set (0.00 sec) mysql> mysql>
6>.查询没学过zhangsan老师课程的学生的学号和姓名
mysql> SELECT sid,sname FROM students WHERE Sid NOT IN (SELECT b.sid FROM course a INNER JOIN score b ON a.id=b.course_id INNER JOIN teacher c ON a.teacher_id=c.id WHERE c.name='Zhang san'); +-----+-----------+ | sid | sname | +-----+-----------+ | 1 | Jason Yin | +-----+-----------+ 1 row in set (0.00 sec) mysql>
7>.查询既学过英语也学过语文的学生的学号和姓名
mysql> SELECT a.sid,sname,count(*) FROM students a INNER JOIN score b ON a.sid=b.sid INNER JOIN course c ON b.course_id=c.id AND c.course_name in ('english', 'chinese') GROUP BY Sid,sname HAVING COUNT(*)>=2; +-----+-----------+----------+ | sid | sname | count(*) | +-----+-----------+----------+ | 1 | Jason Yin | 2 | | 2 | Andy | 2 | | 3 | Bob | 2 | | 7 | Cindy | 2 | +-----+-----------+----------+ 4 rows in set (0.00 sec) mysql>
8>.查询有学生的单科成绩小于60的姓名和课程名称
mysql> mysql> SELECT a.sname,c.course_name FROM students a INNER JOIN score b ON a.sid=b.sid INNER JOIN course c ON b.course_id=c.id WHERE b.score<60; +-----------+-------------+ | sname | course_name | +-----------+-------------+ | Jason Yin | biology | | Bob | math | | John | english | | Cindy | math | +-----------+-------------+ 4 rows in set (0.01 sec) mysql> mysql>
9>.按平均成绩从高到低显示所有学生的姓名和语文，数学，英语 三科成绩
mysql> SELECT a.sid,AVG(score) score_avg,SUM(CASE WHEN b.course_name='chinese' THEN a.score ELSE 0 END) a1,SUM(CASE WHEN b.course_name='math' THEN a.score ELSE 0 END) a2,SUM(CASE WHEN b.course_name='English' THEN a.score ELSE 0 END) a3 FROM score a INNER JOIN course b ON a.course_id=b.id GROUP BY a.sid; +-----+-----------+------+------+------+ | sid | score_avg | a1 | a2 | a3 | +-----+-----------+------+------+------+ | 1 | 76.0000 | 82 | 76 | 90 | | 2 | 78.0000 | 77 | 0 | 78 | | 3 | 79.8000 | 75 | 48 | 95 | | 4 | 72.5000 | 78 | 0 | 0 | | 5 | 82.3333 | 90 | 75 | 0 | | 6 | 73.0000 | 0 | 0 | 58 | | 7 | 64.2000 | 63 | 55 | 65 | | 8 | 94.0000 | 0 | 0 | 0 | +-----+-----------+------+------+------+ 8 rows in set (0.00 sec) mysql>
10>.查询各科成绩中的最高分和最低分
mysql> SELECT course_id,MIN(score),MAX(score) FROM score GROUP BY course_id; +-----------+------------+------------+ | course_id | MIN(score) | MAX(score) | +-----------+------------+------------+ | 1 | 48 | 76 | | 2 | 58 | 95 | | 3 | 63 | 90 | | 5 | 56 | 100 | | 4 | 67 | 92 | +-----------+------------+------------+ 5 rows in set (0.00 sec) mysql> mysql>
11>.计算各科平均成绩和及格率百分比
mysql> SELECT course_id,AVG(score),SUM(CASE WHEN score>=60 THEN 1 ELSE 0 END)/COUNT(*)*100 FROM score GROUP BY course_id; +-----------+------------+---------------------------------------------------------+ | course_id | AVG(score) | SUM(CASE WHEN score>=60 THEN 1 ELSE 0 END)/COUNT(*)*100 | +-----------+------------+---------------------------------------------------------+ | 1 | 63.5000 | 50.0000 | | 2 | 77.2000 | 80.0000 | | 3 | 77.5000 | 100.0000 | | 5 | 76.6000 | 80.0000 | | 4 | 82.0000 | 100.0000 | +-----------+------------+---------------------------------------------------------+ 5 rows in set (0.00 sec) mysql> mysql>
12>.查询不同老师所教不同课程平均分从高到低
mysql> SELECT c.name,b.course_name,AVG(score) FROM score a INNER JOIN course b ON a.course_id=b.id INNER JOIN teacher c ON b.teacher_id=c.id GROUP BY c.name,b.course_name ORDER BY AVG(score) DESC; +-----------+-------------+------------+ | name | course_name | AVG(score) | +-----------+-------------+------------+ | Zhang san | history | 82.0000 | | Liu liu | chinese | 77.5000 | | Li si | english | 77.2000 | | Ding qi | biology | 76.6000 | | Wang wu | math | 63.5000 | +-----------+-------------+------------+ 5 rows in set (0.00 sec) mysql>
13>.查询英语和数学课程成绩排名第5到第10位的学生姓名和成绩
mysql> SELECT c.sname,a.score FROM score a INNER JOIN course b ON a.course_id=b.id INNER JOIN students c ON a.sid=c.sid WHERE b.course_name='English' ORDER BY a.score LIMIT 4,6; +-------+-------+ | sname | score | +-------+-------+ | Bob | 95 | +-------+-------+ 1 row in set (0.00 sec) mysql> mysql>
14>.统计按照各科成绩，分段统计每个课程在90分以上、80-90的、60~80、低于60分的人数
mysql> SELECT b.course_name,SUM(CASE WHEN score>=90 THEN 1 ELSE 0 END),SUM(CASE WHEN score<90 AND score>=80 THEN 1 ELSE 0 END),SUM(CASE WHEN score<80 AND score>=60 THEN 1 ELSE 0 END),SUM(CASE WHEN score<60 THEN 1 ELSE 0 END) FROM score a INNER JOIN course b ON a.course_id=b.id GROUP BY b.course_name; +-------------+--------------------------------------------+---------------------------------------------------------+---------------------------------------------------------+-------------------------------------------+ | course_name | SUM(CASE WHEN score>=90 THEN 1 ELSE 0 END) | SUM(CASE WHEN score<90 AND score>=80 THEN 1 ELSE 0 END) | SUM(CASE WHEN score<80 AND score>=60 THEN 1 ELSE 0 END) | SUM(CASE WHEN score<60 THEN 1 ELSE 0 END) | +-------------+--------------------------------------------+---------------------------------------------------------+---------------------------------------------------------+-------------------------------------------+ | math | 0 | 0 | 2 | 2 | | english | 2 | 0 | 2 | 1 | | chinese | 1 | 1 | 4 | 0 | | biology | 2 | 0 | 2 | 1 | | history | 1 | 4 | 2 | 0 | +-------------+--------------------------------------------+---------------------------------------------------------+---------------------------------------------------------+-------------------------------------------+ 5 rows in set (0.00 sec) mysql> mysql>
15>.查看每门课程被选修的学生数
mysql> SELECT course_id,COUNT(*) FROM score GROUP BY course_id; +-----------+----------+ | course_id | COUNT(*) | +-----------+----------+ | 1 | 4 | | 2 | 5 | | 3 | 6 | | 5 | 5 | | 4 | 7 | +-----------+----------+ 5 rows in set (0.00 sec) mysql> mysql>
16>.查看只学习了一门课程的学生的姓名和学号
mysql> SELECT course_id,COUNT(*) FROM score GROUP BY course_id; +-----------+----------+ | course_id | COUNT(*) | +-----------+----------+ | 1 | 4 | | 2 | 5 | | 3 | 6 | | 5 | 5 | | 4 | 7 | +-----------+----------+ 5 rows in set (0.00 sec) mysql> mysql>
17>.查询名字相同的学生名单和个数
mysql> SELECT sname,count(*) FROM students GROUP BY sname HAVING COUNT(*)>=2; Empty set (0.00 sec) mysql>
18>.85年之后出生的学生人数
mysql> alter table students add brithday datetime; Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> update students set brithday='1983-01-01' where sid<5; Query OK, 4 rows affected (0.01 sec) Rows matched: 4 Changed: 4 Warnings: 0 mysql> update students set brithday='1986-01-01' where sid>=5; Query OK, 4 rows affected (0.01 sec) Rows matched: 4 Changed: 4 Warnings: 0 mysql>
mysql> SELECT * FROM students WHERE brithday>='1985-01-01'; +-----+-------+--------+---------+---------------------+ | sid | sname | gender | dept_id | brithday | +-----+-------+--------+---------+---------------------+ | 5 | Mike | 0 | 2 | 1986-01-01 00:00:00 | | 6 | John | 0 | 3 | 1986-01-01 00:00:00 | | 7 | Cindy | 1 | 3 | 1986-01-01 00:00:00 | | 8 | Susan | 1 | 3 | 1986-01-01 00:00:00 | +-----+-------+--------+---------+---------------------+ 4 rows in set (0.00 sec) mysql> mysql>
19>.查询每门课程的平均成绩，按升序排序，如果平均成绩相同按ID降序排序
mysql> SELECT course_id,AVG(score) FROM score GROUP BY course_id ORDER BY AVG(score),course_id DESC; +-----------+------------+ | course_id | AVG(score) | +-----------+------------+ | 1 | 63.5000 | | 5 | 76.6000 | | 2 | 77.2000 | | 3 | 77.5000 | | 4 | 82.0000 | +-----------+------------+ 5 rows in set (0.00 sec) mysql> mysql>
20>.查询有不及格学生的课程和不及格学生个数
mysql> SELECT course_id,COUNT(*) FROM score WHERE score<60 GROUP BY course_id; +-----------+----------+ | course_id | COUNT(*) | +-----------+----------+ | 5 | 1 | | 1 | 2 | | 2 | 1 | +-----------+----------+ 3 rows in set (0.00 sec) mysql> mysql>
21>.将所有学生姓名中前后的空格去掉
mysql> UPDATE students SET sname=LTRIM(RTRIM(sname)); Query OK, 0 rows affected (0.01 sec) Rows matched: 8 Changed: 0 Warnings: 0 mysql> mysql>
22>.将所有学生的考试成绩展示为课程名:成绩样式
mysql> mysql> SELECT a.sid,CONCAT(b.course_name,':',a.score)FROM score a INNER JOIN course b ON a.course_id=b.id; +-----+-----------------------------------+ | sid | CONCAT(b.course_name,':',a.score) | +-----+-----------------------------------+ | 1 | math:76 | | 1 | english:90 | | 1 | chinese:82 | | 1 | biology:56 | | 2 | english:78 | | 2 | chinese:77 | | 2 | history:92 | | 2 | biology:65 | | 3 | math:48 | | 3 | english:95 | | 3 | chinese:75 | | 3 | history:89 | | 3 | biology:92 | | 4 | chinese:78 | | 4 | history:67 | | 5 | math:75 | | 5 | chinese:90 | | 5 | history:82 | | 6 | english:58 | | 6 | history:88 | | 7 | math:55 | | 7 | english:65 | | 7 | chinese:63 | | 7 | history:68 | | 7 | biology:70 | | 8 | history:88 | | 8 | biology:100 | +-----+-----------------------------------+ 27 rows in set (0.00 sec) mysql>
23>.将所有老师的名字拆分成姓和名两个字段显示
mysql> SELECT name, SUBSTRING(name,1,LOCATE(' ',name)- 1),SUBSTRING(name,LOCATE(' ',name)+1,50) FROM teacher; +-----------+---------------------------------------+---------------------------------------+ | name | SUBSTRING(name,1,LOCATE(' ',name)- 1) | SUBSTRING(name,LOCATE(' ',name)+1,50) | +-----------+---------------------------------------+---------------------------------------+ | Zhang san | Zhang | san | | Li si | Li | si | | Wang wu | Wang | wu | | Liu liu | Liu | liu | | Ding qi | Ding | qi | +-----------+---------------------------------------+---------------------------------------+ 5 rows in set (0.00 sec) mysql> mysql> mysql>
24>.把所有学生的生日格式转换成年月日的格式，并计算每个学生年龄
mysql> SELECT sname,brithday,DATE_FORMAT(brithday, '%Y%m%d'),YEAR(NOW())- YEAR(brithday),FLOOR(DATEDIFF(NOW(),brithday)/365) FROM students; +-----------+---------------------+---------------------------------+-----------------------------+-------------------------------------+ | sname | brithday | DATE_FORMAT(brithday, '%Y%m%d') | YEAR(NOW())- YEAR(brithday) | FLOOR(DATEDIFF(NOW(),brithday)/365) | +-----------+---------------------+---------------------------------+-----------------------------+-------------------------------------+ | Jason Yin | 1983-01-01 00:00:00 | 19830101 | 36 | 36 | | Andy | 1983-01-01 00:00:00 | 19830101 | 36 | 36 | | Bob | 1983-01-01 00:00:00 | 19830101 | 36 | 36 | | Ruth | 1983-01-01 00:00:00 | 19830101 | 36 | 36 | | Mike | 1986-01-01 00:00:00 | 19860101 | 33 | 33 | | John | 1986-01-01 00:00:00 | 19860101 | 33 | 33 | | Cindy | 1986-01-01 00:00:00 | 19860101 | 33 | 33 | | Susan | 1986-01-01 00:00:00 | 19860101 | 33 | 33 | +-----------+---------------------+---------------------------------+-----------------------------+-------------------------------------+ 8 rows in set (0.00 sec) mysql> mysql> mysql>