Question

我必须根据以下表格找到结果

生 StudentPapersSelection为sps StudentGroupManagegemt为sgm 内部数据为iars

从学生我需要学生rollno和名字，其中iars的paperid = sps的paperid和iars groupid = sgm group id和学生ID应该基于前两件事。

我正在运行的查询是：

select students.rollno, students.name 
from students,sps,iars,sgm 
where iars.id=1
and students.studentid=(select studentid 
                        from sps where sps.paperid=iars.paperid
                        and iars.id=1)
and students.studentid=(select studentid 
                        from sgm 
                        where sgm.groupid=iars.groupid 
                        and iars.id=1) 
and students.course=iars.courseid  
and students.semester=iars.semester

它表示查询返回超过1行。我讨厌这个问题。

Answer 1

根据您的评论和问题中的有限信息判断，您似乎想要做的不是

...students.studentid=(select studentid ...

是用

替换两个出现

...students.studentid in(select studentid ...

所以你的查询应该是这样的：

select students.rollno, students.name from students,sps,iars,sgm where iars.id=1
    and students.studentid in (select studentid from sps 
        where sps.paperid=iars.paperid and iars.id=1) 
    and students.studentid in (select studentid from sgm
        where sgm.groupid=iars.groupid and iars.id=1) 
    and students.course=iars.courseid 
    and students.semester=iars.semester

Answer 2

我会试着猜：

select  students.rollno,
        students.name
from    iars, students join sps on students.studentid = sps.studentid
        join sgm on students.studentid = sgm.studentid
where   iars.id = 1 
and     sps.paperid=iars.paperid
and     sgm.groupid=iars.groupid
and     students.course = iars.courseid
and     students.semester = iars.semester

假设这样的表：

CREATE TABLE `students` (
  `studentid` int(11) NOT NULL AUTO_INCREMENT,
  `rollno` int(11) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `course` int(11) DEFAULT NULL,
  `semester` int(11) DEFAULT NULL,
  PRIMARY KEY (`studentid`)
) ENGINE=InnoDB AUTO_INCREMENT=66820 DEFAULT CHARSET=latin1


CREATE TABLE `sps` (
  `studentid` int(11) NOT NULL AUTO_INCREMENT,
  `paperid` int(11) DEFAULT NULL,
  PRIMARY KEY (`studentid`)
) ENGINE=InnoDB AUTO_INCREMENT=66820 DEFAULT CHARSET=latin1


CREATE TABLE `sgm` (
  `studentid` int(11) NOT NULL AUTO_INCREMENT,
  `groupid` int(11) DEFAULT NULL,
  PRIMARY KEY (`studentid`)
) ENGINE=InnoDB AUTO_INCREMENT=66820 DEFAULT CHARSET=latin1


CREATE TABLE `iars` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `paperid` int(11) DEFAULT NULL,
  `groupid` int(11) DEFAULT NULL,
  `courseid` int(11) DEFAULT NULL,
  `semester` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=66820 DEFAULT CHARSET=latin1

这样的数据：

insert into students values (1,1,'a',1,1);
insert into students values (2,1,'b',1,1);
insert into iars values(1,1,1,1,1);
insert into sgm values (1,1);
insert into sps values (1,1);

无法运行查询

2 个答案: