SQL基础复习回顾

今年的几次校招笔试都考了数据库的相关知识，发现自己平时在项目中copy代码copy习惯了，在考场上连最简单的SQL都写不出来，真是醉过！特意花了点时间，在网上找了相关题目，补习了一下SQL相关基础。

假如有一个教务管理系统模型，该模型由学生表db_student、教师表db_teacher、课程表db_course、成绩表db_score四张表组成。表的具体结构如下：

学生表db_student

 

教师表db_teacher

 

课程表db_course

 

成绩表db_score

 

下面我们用SQL语句来创建这四张表，并往里面插入测试数据。

创建表语句：

CREATE TABLE db_student (sNo VARCHAR (3) NOT NULL COMMENT '学生编号',sName VARCHAR (4) NOT NULL COMMENT '学生姓名',sSex VARCHAR (2) NOT NULL COMMENT '学生性别',sBirthday DATETIME COMMENT '学生生日',class VARCHAR (5) COMMENT '班级');CREATE TABLE db_course (cNo VARCHAR (5) NOT NULL COMMENT '课程编号',cName VARCHAR (10) NOT NULL COMMENT '课程名',tNo VARCHAR (10) NOT NULL COMMENT '学生编号');CREATE TABLE db_score (sNo VARCHAR (3) NOT NULL COMMENT '学生编号',cNo VARCHAR (5) NOT NULL COMMENT '课程编号',degree NUMERIC (10, 1) NOT NULL COMMENT '分数',);CREATE TABLE db_teacher (tNo VARCHAR (3) NOT NULL COMMENT '教师编号',tName VARCHAR (4) NOT NULL COMMENT '教师名字',tSex VARCHAR (2) NOT NULL COMMENT '教师性别',tBirthday DATETIME NOT NULL COMMENT '教师生日',prof VARCHAR (6) COMMENT '职称',depart VARCHAR (10) NOT NULL COMMENT '所在学部');

往db_student表里插入测试数据语句：

INSERT INTO db_student (sNo,sName,sSex,sBirthday,class) VALUES (108 ,'曾华','男' ,'1977-09-01',95033);INSERT INTO db_student (sNo,sName,sSex,sBirthday,class) VALUES (105 ,'匡明','男' ,'1975-10-02',95031);INSERT INTO db_student (sNo,sName,sSex,sBirthday,class) VALUES (107 ,'王丽','女' ,'1976-01-23',95033);INSERT INTO db_student (sNo,sName,sSex,sBirthday,class) VALUES (101 ,'李军','男' ,'1976-02-20',95033);INSERT INTO db_student (sNo,sName,sSex,sBirthday,class) VALUES (109 ,'王芳','女' ,'1975-02-10',95031);INSERT INTO db_student (sNo,sName,sSex,sBirthday,class) VALUES (103 ,'陆君','男' ,'1974-06-03',95031);

往db_course表里插入测试数据语句：

INSERT INTO db_course(cNo,cName,tNo)VALUES ('3-105','计算机导论',825);INSERT INTO db_course(cNo,cName,tNo)VALUES ('3-245','操作系统',804);INSERT INTO db_course(cNo,cName,tNo)VALUES ('6-166','数据电路',856);INSERT INTO db_course(cNo,cName,tNo)VALUES ('9-888','高等数学',100);

往db_score表里插入测试数据语句：

INSERT INTO db_score(sNo,cNo,degree)VALUES (103,'3-245',86);INSERT INTO db_score(sNo,cNo,degree)VALUES (105,'3-245',75);INSERT INTO db_score(sNo,cNo,degree)VALUES (109,'3-245',68);INSERT INTO db_score(sNo,cNo,degree)VALUES (103,'3-105',92);INSERT INTO db_score(sNo,cNo,degree)VALUES (105,'3-105',88);INSERT INTO db_score(sNo,cNo,degree)VALUES (109,'3-105',76);INSERT INTO db_score(sNo,cNo,degree)VALUES (101,'3-105',64);INSERT INTO db_score(sNo,cNo,degree)VALUES (107,'3-105',91);INSERT INTO db_score(sNo,cNo,degree)VALUES (108,'3-105',78);INSERT INTO db_score(sNo,cNo,degree)VALUES (101,'6-166',85);INSERT INTO db_score(sNo,cNo,degree)VALUES (107,'6-106',79);INSERT INTO db_score(sNo,cNo,degree)VALUES (108,'6-166',81);

往db_teacher表里插入测试数据语句：

INSERT INTO db_teacher(tNo,tName,tSex,tBirthday,prof,depart)VALUES (804,'李诚','男','1958-12-02','副教授','计算机系');INSERT INTO db_teacher(tNo,tName,tSex,tBirthday,prof,depart)VALUES (856,'张旭','男','1969-03-12','讲师','电子工程系');INSERT INTO db_teacher(tNo,tName,tSex,tBirthday,prof,depart)VALUES (825,'王萍','女','1972-05-05','助教','计算机系');INSERT INTO db_teacher(tNo,tName,tSex,tBirthday,prof,depart)VALUES (831,'刘冰','女','1977-08-14','助教','电子工程系');

下面我们写出下面43个问题的SQL语句

-- 1、查询db_student表中的所有记录的sName、sSex和class列。

SELECT sName,sSex,class FROM db_student

-- 2、查询教师所有的单位即不重复的depart列。

SELECT DISTINCT depart FROM db_teacher

-- 3、查询db_student表的所有记录。

SELECT * FROM db_student

-- 4、查询db_score表中成绩在60到80之间的所有记录。

SELECT * FROM db_score WHERE degree BETWEEN 60 AND 80

-- 5、查询db_score表中成绩为85，86或88的记录。

SELECT * FROM db_score WHERE degree IN (85,86,88)

 -- 6、查询db_student表中“95031”班或性别为“女”的同学记录。

SELECT * FROM db_student WHERE class='95031' OR sSex='女'

-- 7、以class降序查询db_student表的所有记录。

SELECT * FROM db_student ORDER BY class DESC

-- 8、以cNo升序、degree降序查询db_score表的所有记录。

SELECT * FROM db_score ORDER BY cNo ASC,degree DESC

-- 9、查询“95031”班的学生人数。

SELECT COUNT(*) FROM db_student WHERE class='95031'

-- 10、查询db_score表中的最高分的学生学号和课程号。

SELECT sNo,cNo FROM db_score WHERE degree=(SELECT MAX(degree) FROM db_score)解法二：SELECT sNo,cNO FROM db_score ORDER BY degree DESC LIMIT 1

-- 11、查询‘3-105’号课程的平均分。

SELECT AVG(degree) FROM db_score WHERE cNo='3-105'

-- 12、查询db_score表中至少有5名学生选修的并以3开头的课程的平均分数。

SELECT AVG(degree),cNo FROM db_score WHERE cNo LIKE '3%' GROUP BY cNo HAVING COUNT(sNo)>=5

-- 13、查询最低分大于70，最高分小于90的sNo列。

SELECT sNo FROM db_score GROUP BY sNo HAVING MIN(degree)>70 AND MAX(degree)<90

-- 14、查询所有学生的sName、cNo和degree列。

SELECT st.sName,sc.cNo,sc.degree FROM db_student st,db_score sc WHERE st.sNo=sc.sNo

-- 15、查询所有学生的sNo、cName和degree列。

SELECT s.sNo,c.cName,s.degree FROM db_course c,db_score s WHERE c.cNo=s.cNo

-- 16、查询所有学生的sName、cName和degree列。

SELECT st.sName,c.cName,sc.degree FROM db_course c,db_score sc,db_student st WHERE c.cNo=sc.cNo AND sc.sNo=st.sNo

-- 17、查询“95033”班所选课程的平均分。

SELECT AVG(sc.degree) FROM db_student st,db_score sc WHERE st.sNo=sc.sNoAND st.class='95033'

-- 18、查询选修“3-105”课程,且成绩高于“109”号同学成绩的所有同学的记录。

SELECT * FROM db_score WHERE cNo='3-105' AND degree>ALL(SELECT degree FROM db_score WHERE sNo='109')

-- 19、查询db_score表中选学一门以上课程的同学中分数为非最高分成绩的记录。

SELECT * FROM db_score WHERE degree!=(SELECT MAX(degree) FROM db_score) GROUP BY sNo HAVING COUNT(SNO)>1

 -- 20、查询和学号为108的同学同年出生的所有学生的sNo、sName和sBirthday列。

SELECT sNo,sName,sBirthday FROM db_student WHERE YEAR(sBirthday)=(SELECT YEAR(sBirthday) FROM db_student WHERE sNo='108')

-- 21、查询“张旭“教师任课的学生成绩。

SELECT sc.sNo,sc.degree,t.tName FROM db_course c,db_score sc,db_teacher t WHERE c.cNo=sc.cNo AND c.tNo=t.tNo AND t.tName='张旭'

-- 22、查询选修某课程的同学人数多于5人的教师姓名。

SELECT t.tName FROM db_teacher t,db_course c,db_score sc WHERE t.tNo=c.tNo AND c.cNo=sc.cNo GROUP BY c.cNo HAVING COUNT(c.cNo)>5

-- 23、查询95033班和95031班全体学生的记录。

SELECT * FROM db_student st,db_course c,db_score sc WHERE st.sNo=sc.sNo AND c.cNo=sc.cNo  AND st.class IN (95033,95031)

-- 24、查询存在有85分以上成绩的课程cNo.

SELECT cNo FROM db_score GROUP BY cNo HAVING MAX(degree)>85

-- 25、查询出“计算机系“教师所教课程的成绩表。

SELECT * FROM db_course c,db_score sc,db_teacher t WHERE c.cNo=sc.cNo AND c.tNo=t.tNo AND t.depart='计算机系'

-- 26、查询“计算机系”与“电子工程系“不同职称的教师的tName和prof。

SELECT tName,prof FROM db_teacher WHERE depart='计算机系' AND prof NOT IN(SELECT prof FROM db_student WHERE depart='电子工程系')

-- 27、查询选修编号为“3-105“课程且成绩至少高于选修编号为“3-245”的同学的cNo、sNo和degree,并按degree从高到低次序排序。

SELECT * FROM db_score WHERE cNo='3-105' AND degree>ANY(SELECT degree FROM db_score WHERE cNo='3-245') ORDER BY degree DESC

-- 28、查询选修编号为“3-105”且成绩高于选修编号为“3-245”课程的同学的cNo、sNo和degree.

SELECT * FROM db_score WHERE cNo='3-105' AND degree>ALL(SELECT degree FROM db_score WHERE cNo='3-245')

-- 29、查询所有教师和同学的name、sex和birthday.

SELECT tName AS name,tSex AS sex,tBirthday AS birthday FROM db_teacherUNIONSELECT sName AS name,sSex AS sex,sBirthday AS birthday FROM db_student

-- 30、查询所有“女”教师和“女”同学的name、sex和birthday.

SELECT tName AS name,tSex AS sex,tBirthday AS birthday FROM db_teacher WHERE tSex='女'UNIONSELECT sName AS name,sSex AS sex,sBirthday AS birthday FROM db_student WHERE sSex='女'

-- 31、查询成绩比该课程平均成绩低的同学的成绩表。

注意题目强调的是该课程平均成绩，并不是所有课程平均成绩。

SELECT s1.* FROM db_score s1 WHERE s1.degree<(SELECT AVG(s2.degree) FROM db_score s2 WHERE s1.cNo=s2.cNo)

-- 32、查询所有任课教师的tName和depart.

题目中说的是任课教师，教师表里可能有的教师没有任课。任课的教师的tNo都在课程表里。

SELECT t.tName,t.depart FROM db_teacher t,db_course c WHERE t.tNo=c.tNo解法2：SELECT tName,depart FROM db_teacher WHERE tNo IN (SELECT tNo FROM db_course)

-- 33 查询所有未讲课的教师的tNname和depart. 

SELECT tName,depart FROM db_teacher t LEFT JOIN db_course c USING(tNo) WHERE ISNULL(c.tNo)解法2：SELECT tName,depart FROM db_teacher WHERE tNo NOT IN(SELECT tNo FROM db_course)

第一种解法貌似更好，使用NOT IN语句扫描次数比较多。

-- 34、查询至少有2名男生的班号。

SELECT class FROM db_student WHERE sSex='男' GROUP BY class HAVING COUNT(sSex)>=2

-- 35、查询db_student表中不姓“王”的同学记录。

SELECT * FROM db_student WHERE sName NOT LIKE '王%'

-- 36、查询db_student表中每个学生的姓名和年龄。

SELECT sName,YEAR(NOW())-YEAR(sBirthday) AS age FROM db_student

-- 37、查询db_student表中最大和最小的sBirthday日期值。

SELECT MAX(sBirthday),MIN(sBirthday) FROM db_student

-- 38、以班号和年龄从大到小的顺序查询Student表中的全部记录。

SELECT class,YEAR(NOW())-YEAR(sBirthday) AS age FROM db_student ORDER BY class DESC,age DESC

-- 39、查询“男”教师及其所上的课程。

SELECT t.tName,c.cName FROM db_teacher t,db_course c WHERE t.tNo=c.tNo AND t.tSex='男'

-- 40、查询最高分同学的sNo、cNo和degree列。

SELECT sNo,cNo,degree FROM db_score WHERE degree=(SELECT MAX(degree) FROM db_score)

-- 41、查询和“李军”同性别的所有同学的sName.

SELECT sName FROM db_student WHERE sSex=(SELECT sSex FROM db_student WHERE sName='李军')

-- 42、查询和“李军”同性别并同班的同学sName.

SELECT sName FROM db_student WHERE sSex=(SELECT sSex FROM db_student WHERE sName='李军') AND class=(SELECT class FROM db_student WHERE sName='李军')

-- 43、查询所有选修“计算机导论”课程的“男”同学的成绩表

SELECT sc.* FROM db_course c,db_score sc,db_student st WHERE c.cNo=sc.cNo AND sc.sNo=st.sNo AND c.cName='计算机导论' AND st.sSex='男'

可以使用USING关键字对连接进行简化

在SQL/92标准可以使用USING子句对连接条件进行简化，但是只有在查询满足以下两个条件时才能给使用USING进行简化：

1、查询必须是等连接的

2、等连接中的列必须是同名

解法2：SELECT sc.* FROM db_score sc JOIN (db_course c,db_student st) USING (sNo,cNo) WHERE c.cName='计算机导论' AND st.sSex='男'

相信仔细弄透了这43个题，对SQL基础知识会有初步的了解。应付校园招聘SQL笔试题应该问题不大。

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