查询指定列
[例1] 查询全体学生的学号与姓名。
SELECT Sno,Sname
FROM Student;
[例2] 查询全体学生的姓名、学号、所在系。
SELECT Sname,Sno,Sdept
FROM Student;
[例3] 查询全体学生的详细记录。
SELECT Sno,Sname,Ssex,Sage,Sdept
FROM Student;
或
SELECT *
FROM Student;
[例4] 查全体学生的姓名及其出生年份。
SELECT Sname,2004-Sage /*假定当年的年份为2004年*/ FROM Student;
[例5] 查询全体学生的姓名、出生年份和所有系,要求用小 写字母表示所有系名
SELECT Sname,„Year of Birth: ‘,2004-Sage,
ISLOWER(Sdept)
FROM Student;
[例6] 查询选修了课程的学生学号。
SELECT Sno FROM SC;
等价于:
SELECT ALL Sno FROM SC;
[例7] 查询计算机科学系全体学生的名单。
SELECT Sname www.111com.net
FROM Student
WHERE Sdept=„CS‟;
[例8] 查询所有年龄在20岁以下的学生姓名及其年龄。 SELECT Sname,Sage
FROM Student
WHERE Sage < 20;
[例9] 查询考试成绩有不及格的学生的学号。
SELECT DISTINCT Sno
FROM SC
WHERE Grade<60;
[例10] 查询年龄在20~23岁(包括20岁和23岁)之间的学生的 姓名、系别和年龄
SELECT Sname,Sdept,Sage
FROM Student
WHERE Sage BETWEEN 20 AND 23;
[例11] 查询年龄不在20~23岁之间的学生姓名、系别和年龄
SELECT Sname,Sdept,Sage
FROM Student
WHERE Sage NOT BETWEEN 20 AND 23;
[例12]查询信息系(IS)、数学系(MA)和计算机科学系(CS)学生的姓名和 性别。
SELECT Sname,Ssex
FROM Student
WHERE Sdept IN ( ‘IS’,’MA’,’CS’ );
[例13]查询既不是信息系、数学系,也不是计算机科学系的学生的姓名和性别。 SELECT Sname,Ssex
FROM Student
WHERE Sdept NOT IN ( ‘IS’,’MA’,’CS’ );
[例14] 查询学号为200215121的学生的详细情况。
SELECT *
FROM Student
WHERE Sno LIKE „200215121′;
等价于:
SELECT *
FROM Student
WHERE Sno = ‘ 200215121 ‘;
[例15] 查询所有姓刘学生的姓名、学号和性别。
SELECT Sname,Sno,Ssex
FROM Student
WHERE Sname LIKE „刘%‟;
[例16] 查询姓”欧阳”且全名为三个汉字的学生的姓名。
SELECT Sname
FROM Student
WHERE Sname LIKE ‘欧阳__’;
[例17] 查询名字中第2个字为”阳”字的学生的姓名和学号。
SELECT Sname,Sno
FROM Student
WHERE Sname LIKE „__阳%‟;
[例18] 查询所有不姓刘的学生姓名。
SELECT Sname,Sno,Ssex
FROM Student
WHERE Sname NOT LIKE ‘刘%’;
[例19] 查询DB_Design课程的课程号和学分。
SELECT Cno,Ccredit
FROM Course
WHERE Cname LIKE ‘DB_Design’ ESCAPE ‘„;
[例20] 查询以”DB_”开头,且倒数第3个字符为 i的课程的详细情况。 SELECT *
FROM Course
WHERE Cname LIKE ‘DB_%i_ _’ ESCAPE ‘ „;
[例21] 某些学生选修课程后没有参加考试,所以有选课记录,但没 有考试成绩。查询缺少成绩的学生的学号和相应的课程号。 SELECT Sno,Cno
FROM SC
WHERE Grade IS NULL
[例22] 查所有有成绩的学生学号和课程号。
SELECT Sno,Cno
FROM SC
WHERE Grade IS NOT NULL;
[例23] 查询计算机系年龄在20岁以下的学生姓名。
SELECT Sname
FROM Student
WHERE Sdept= ‘CS’ AND Sage<20;
改写[例12]
[例12] 查询信息系(IS)、数学系(MA)和计算机科学系 (CS)学生的姓名和性别。
SELECT Sname,Ssex
FROM Student
WHERE Sdept IN ( ‘IS’,’MA’,’CS’ )
可改写为:
SELECT Sname,Ssex
FROM Student
WHERE Sdept= ‘ IS ‘ OR Sdept= ‘ MA’ OR Sdept= ‘ CS ‘;
[例24] 查询选修了3号课程的学生的学号及其成绩,查询结果按分 数降序排列。
SELECT Sno,Grade
FROM SC
WHERE Cno= ‘ 3 ‘
ORDER BY Grade DESC;
[例25] 查询全体学生情况,查询结果按所在系的系号升序排 列,同一系中的学生按年龄降序排列。
SELECT *
FROM Student
ORDER BY Sdept,Sage DESC;
[例26] 查询学生总人数。
SELECT COUNT(*)
FROM Student;
[例27] 查询选修了课程的学生人数。
SELECT COUNT(DISTINCT Sno)
FROM SC;
[例28] 计算1号课程的学生平均成绩。
SELECT AVG(Grade)
FROM SC
WHERE Cno= ‘ 1 ‘;
[例29] 查询选修1号课程的学生最高分数。
SELECT MAX(Grade)
FROM SC
WHER Cno= „ 1 ‟;
[例30]查询学生200215012选修课程的总学分数。
SELECT SUM(Ccredit)
FROM SC, Course
WHER Sno=’200215012′ AND SC.Cno=Course.Cno;
[例31] 求各个课程号及相应的选课人数。
SELECT Cno,COUNT(Sno)
FROM SC
GROUP BY Cno;
[例32] 查询选修了3门以上课程的学生学号。
SELECT Sno
FROM SC
GROUP BY Sno
HAVING COUNT(*) >3;
[例33] 查询每个学生及其选修课程的情况
SELECT Student.*,SC.*
FROM Student,SC
WHERE Student.Sno = SC.Sno;
[例34] 对[例33]用自然连接完成。
SELECT Student.Sno,Sname,Ssex,Sage,Sdept,Cno,Grade FROM Student,SC
WHERE Student.Sno = SC.Sno;
[例35]查询每一门课的间接先修课(即先修课的先修课)
SELECT FIRST.Cno,SECOND.Cpno
FROM Course FIRST,Course SECOND
WHERE FIRST.Cpno = SECOND.Cno;
[例 36] 改写[例33]
SELECT Student.Sno,Sname,Ssex,Sage,Sdept,Cno,Grade FROM Student LEFT OUT JOIN SC ON (Student.Sno=SC.Sno);
[例37]查询选修2号课程且成绩在90分以上的所有学生
SELECT Student.Sno, Sname
FROM Student, SC
WHERE Student.Sno = SC.Sno AND
/* 连接谓词*/
SC.Cno= „2‟ AND SC.Grade > 90; /* 其他限定条件 */
[例38]查询每个学生的学号、姓名、选修的课程名及成绩
SELECT Student.Sno,Sname,Cname,Grade
FROM Student,SC,Course /*多表连接*/
WHERE Student.Sno = SC.Sno
and SC.Cno = Course.Cno;
[例39] 查询与“刘晨”在同一个系学习的学生。
此查询要求可以分步来完成
① 确定“刘晨”所在系名
SELECT Sdept
FROM Student WHERE Sname= ‘ 刘晨 ‘;
结果为: CS
② 查找所有在IS系学习的学生。
SELECT Sno,Sname,Sdept
FROM Student
WHERE Sdept= ‘ CS ‘;
将第一步查询嵌入到第二步查询的条件中
SELECT Sno,Sname,Sdept
FROM Student
WHERE Sdept IN
(SELECT Sdept
FROM Student
WHERE Sname= „ 刘晨 ‟);
此查询为不相关子查询。
用自身连接完成[例39]查询要求
SELECT S1.Sno,S1.Sname,S1.Sdept
FROM Student S1,Student S2
WHERE S1.Sdept = S2.Sdept AND
S2.Sname = ‘刘晨’;
[例40]查询选修了课程名为“信息系统”的学生学号和姓名 SELECT Sno,Sname ③ 最后在Student关系中 FROM Student 取出Sno和Sname WHERE Sno IN
(SELECT Sno ② 然后在SC关系中找出选 FROM SC 修了3号课程的学生学号 WHERE Cno IN
(SELECT Cno ① 首先在Course关系中找出 FROM Course “信息系统”的课程号,为3号 WHERE Cname= „信息系统‟
)
);
用连接查询实现[例40]
SELECT Sno,Sname
FROM Student,SC,Course
WHERE Student.Sno = SC.Sno AND
SC.Cno = Course.Cno AND
Course.Cname=„信息系统‟;
例:假设一个学生只可能在一个系学习,并且必须属于一个 系,则在[例39]可以用 = 代替IN :
SELECT Sno,Sname,Sdept
FROM Student
WHERE Sdept =
(SELECT Sdept
FROM Student
WHERE Sname= „刘晨‟);
[例41]找出每个学生超过他选修课程平均成绩的课程
号。
SELECT Sno, Cno
FROM SC x
WHERE Grade >=(SELECT AVG(Grade)
FROM SC y
WHERE y.Sno=x.Sno);
[例42] 查询其他系中比计算机科学某一学生年龄
小的学生姓名和年龄
SELECT Sname,Sage
FROM Student
WHERE Sage < ANY (SELECT Sage
FROM Student WHERE Sdept= ‘ CS ‘) AND Sdept <> „CS ‘ ; /*父查询块中 的条件 */
用聚集函数实现[例42]
SELECT Sname,Sage
FROM Student
WHERE Sage <
(SELECT MAX(Sage)
FROM Student www.111com.net
WHERE Sdept= „CS ‘)
AND Sdept <> ‘ CS ‟;
[例43] 查询其他系中比计算机科学系所有学生年龄都小 的学生姓名及年龄。
方法一:用ALL谓词
SELECT Sname,Sage
FROM Student
WHERE Sage < ALL
(SELECT Sage
FROM Student
WHERE Sdept= ‘ CS ‘)
AND Sdept <> ‘ CS ‟;
方法二:用聚集函数
SELECT Sname,Sage
FROM Student
WHERE Sage <
(SELECT MIN(Sage)
FROM Student
WHERE Sdept= ‘ CS ‘)
AND Sdept <>’ CS ‟;
[例44]查询所有选修了1号课程的学生姓名。
用嵌套查询
SELECT Sname
FROM Student
WHERE EXISTS
(SELECT *
FROM SC
WHERE Sno=Student.Sno AND Cno= ‘ 1 ‘);
用连接运算
SELECT Sname
FROM Student, SC
WHERE Student.Sno=SC.Sno AND SC.Cno= ’1′;
[例45] 查询没有选修1号课程的学生姓名。
SELECT Sname
FROM Student
WHERE NOT EXISTS
(SELECT *
FROM SC
WHERE Sno = Student.Sno AND Cno=’1′);
[例39]查询与“刘晨”在同一个系学习的学生。
可以用带EXISTS谓词的子查询替换:
SELECT Sno,Sname,Sdept
FROM Student S1
WHERE EXISTS
(SELECT *
FROM Student S2
WHERE S2.Sdept = S1.Sdept AND
S2.Sname = „刘晨‟);
[例46] 查询选修了全部课程的学生姓名。
SELECT Sname
FROM Student
WHERE NOT EXISTS
(SELECT *
FROM Course
WHERE NOT EXISTS
(SELECT *
FROM SC
WHERE Sno= Student.Sno AND Cno= Course.Cno )
);
[例47]查询至少选修了学生200215122选修的全部课程的学
生号码。
用NOT EXISTS谓词表示:
SELECT DISTINCT Sno
FROM SC SCX
WHERE NOT EXISTS
(SELECT *
FROM SC SCY
WHERE SCY.Sno = ‘ 200215122 ‘ AND
NOT EXISTS
(SELECT *
FROM SC SCZ
WHERE SCZ.Sno=SCX.Sno AND
SCZ.Cno=SCY.Cno));
[例48] 查询计算机科学系的学生及年龄不大于19岁的学生。
方法一:
� SELECT *
� FROM Student
� WHERE Sdept= ‘CS’
� UNION
� SELECT *
� FROM Student
� WHERE Sage<=19;
方法二:
SELECT DISTINCT *
FROM Student
WHERE Sdept= ‘CS’ OR Sage<=19;
[例49] 查询选修了课程1或者选修了课程2的学生。
SELECT Sno
FROM SC
WHERE Cno=’ 1 ‘
UNION
SELECT Sno
FROM SC
WHERE Cno= ‘ 2 ‘;
[例50] 查询计算机科学系的学生与年龄不大于19岁
的学生的交集
SELECT *
FROM Student
WHERE Sdept=’CS’
INTERSECT
SELECT *
FROM Student
WHERE Sage<=19
注:sql server 无交运算
[例50] 实际上就是查询计算机科学系中年龄不大
于19岁的学生
SELECT *
FROM Student
WHERE Sdept= „CS‟ AND Sage<=19;
[例51] 查询选修课程1的学生集合与选修课程2的学生集
合的交集
SELECT Sno
FROM SC
WHERE Cno=’ 1 ‘
INTERSECT
SELECT Sno
FROM SC
WHERE Cno=’2 ‘;
[例51]实际上是查询既选修了课程1又选修了课程2
的学生
SELECT Sno
FROM SC
WHERE Cno=’ 1 ‘ AND Sno IN
(SELECT Sno FROM SC
WHERE Cno=’ 2 ‘);
[例52] 查询计算机科学系的学生与年龄不大于19岁的学
生的差集。
SELECT *
FROM Student
WHERE Sdept=’CS’
EXCEPT
SELECT *
FROM Student
WHERE Sage <=19;
注:sql server 无差运算
[例52]实际上是查询计算机科学系中年龄大于19岁
的学生
SELECT *
FROM Student
WHERE Sdept= ‘CS’ AND Sage>19;