2

这是我的表格和插入值：

create table student (


LastName      varchar(40),
  FirstName     varchar(40),
  SID           number(5),
  SSN           number(9),
  Career        varchar(4),
  Program       varchar(10),
  City          varchar(40),
  Started       number(4),

  primary key (SID),
  unique(SSN)
);
create table enrolled (
  StudentID     number(5),
  CourseID      number(4),
  Quarter       varchar(6),
  Year          number(4),

  primary key (StudentID, CourseID),
  foreign key (StudentID) references student(SID),
  foreign key (CourseID) references course(CID)
);
insert into student
    values ( 'Brennigan', 'Marcus', 90421, 987654321, 'UGRD', 'COMP-GPH', 'Evanston', 2001 );
insert into student
    values ( 'Patel', 'Deepa', 14662, null, 'GRD', 'COMP-SCI', 'Evanston', 2003 );
insert into student
    values ( 'Snowdon', 'Jonathan', 08871, 123123123, 'GRD', 'INFO-SYS', 'Springfield', 2005 );
insert into student
    values ( 'Starck', 'Jason', 19992, 789789789, 'UGRD', 'INFO-SYS', 'Springfield', 2003 );
insert into student
    values ( 'Johnson', 'Peter', 32105, 123456789, 'UGRD', 'COMP-SCI', 'Chicago', 2004 );
insert into student
    values ( 'Winter', 'Abigail', 11035, 111111111, 'GRD', 'PHD', 'Chicago', 2003 );
insert into student
    values ( 'Patel', 'Prakash', 75234, null, 'UGRD', 'COMP-SCI', 'Chicago', 2001 );
insert into student
    values ( 'Snowdon', 'Jennifer', 93321, 321321321, 'GRD', 'COMP-SCI', 'Springfield', 2004 );
insert into enrolled
    values (11035, 1020, 'Fall', 2005);
insert into enrolled
    values (11035, 1092, 'Fall', 2005);
insert into enrolled
    values (11035, 8772, 'Spring', 2006);
insert into enrolled
    values (75234, 3201, 'Winter', 2006);
insert into enrolled
    values (08871, 1092, 'Fall', 2005);
insert into enrolled
    values (90421, 8772, 'Spring', 2006);
insert into enrolled
    values (90421, 2987, 'Spring', 2006);

我有以下查询：

SELECT e.studentid
FROM enrolled e 
FULL OUTER JOIN student s ON e.studentid = s.sid 
WHERE ((e.quarter = 'Fall') OR (e.quarter = 'Spring')) 
GROUP BY e.studentid 
HAVING count(e.studentid) = 1;

但这只会返回

8871

这应该返回

8871
90421

此查询的目标是：列出在秋季学期注册了至少一门课程或在春季学期注册了至少一门课程的学生，但不能同时注册两者。您必须添加几行来测试您的查询。

任何帮助将不胜感激。谢谢。

4

3 回答 3

3

试试这个，

SELECT  a.SID
FROM    student a
        INNER JOIN enrolled b
            ON a.SID = b.StudentID
WHERE   b.quarter IN ('Fall', 'Spring')
GROUP   BY a.SID
HAVING  COUNT(DISTINCT b.quarter) = 1
于 2013-04-25T06:10:32.297 回答
2 
SELECT  e.studentid
FROM    enrolled e 
WHERE   e.quarter IN ('Spring', 'Fall')
GROUP BY
        e.studentid 
HAVING  COUNT(DISTINCT quarter) = 1;

90421在春季期间参加了两门不同的课程，这就是为什么您的原始查询计算了两次。

您需要计算季节，而不是入学人数。

于 2013-04-25T06:11:17.833 回答
0

学生 ID 有两条记录 - 90421 因此计数将返回 2

于 2013-04-25T06:13:15.157 回答