选择两个不同值的最小值

Question

我正在进行sql选择,我需要获取ID的所有最小记录.我的问题是,虽然我认为我的代码正在运行,但它通常会返回其他列的错误值,显然是因为我没有使用必须支持我的聚合min函数.这是我的代码.

SELECT *
FROM example_students
INNER JOIN
(SELECT  id, student, test, subject, MIN(score), semester
FROM example_student_scores
WHERE studentid=94
GROUP BY studentid, test, subject) as scores
ON example_students.id=scores.studentid

这就是我想要我的代码.

从exampletable中选择每个不同测试和学科组合的最低分数,其中学生的身份编号为#94

以下是该示例的两个(经过大量修改的)表(我在这里和我的代码中也更改了所有列名).

example_students
id    name
----+-----------+
94    Bob
1023  Thomas

.

example_students_scores
id    studentId     test       subject     score       semester
----+-----------+-----------+-----------+-----------+-----------

0    94          quiz        math        46          fall
1    94          quiz        math        71          fall
2    94          quiz        math        63          winter
3    94          midterm     math        94          winter
4    94          midterm     science     72          fall
5    94          quiz        math        50          spring
6    94          final       math        76          spring
7    1023        quiz        math        6           spring
8    1023        quiz        math        52          winter
9    1023        quiz        science     68          fall
..*

结果应该是

results
id    studentId     test       subject     score       semester
----+-----------+-----------+-----------+-----------+-----------
0    94          quiz        math        46          fall
3    94          midterm     math        94          winter
4    94          midterm     science     72          fall
6    94          final       math        76          spring

问题是,我将得到学期列的错误值(以及我在实际工作中的所有其他列).

鉴于这需要很长时间才能得到无处,这里是sql来创建两个示例数据库:

drop table if exists example_students;
drop table if exists example_students_scores;
create table example_students(
    id int(10) primary key,
    name char(25)
);
create table example_students_scores(
    id int(10) not null,
    studentId int(10) not null,
    test char(20),
    subject char(20),
    score int(10) not null default '0',
    semester char(20),
    primary key (id),
    index studentid (studentid)
);
insert into example_students values ('94','Bob');
insert into example_students values ('1023','Thomas');
insert into example_students_scores values ('0'    ,'94'          ,'quiz'        ,'math'        ,'46'          ,'fall');
insert into example_students_scores values ('1'    ,'94'          ,'quiz'        ,'math'        ,'71'          ,'fall');
insert into example_students_scores values ('2'    ,'94'          ,'quiz'        ,'math'        ,'63'          ,'winter');
insert into example_students_scores values ('3'    ,'94'          ,'midterm'     ,'math'        ,'94'          ,'winter');
insert into example_students_scores values ('4'    ,'94'          ,'midterm'     ,'science'     ,'72'          ,'fall');
insert into example_students_scores values ('5'    ,'94'          ,'quiz'        ,'math'        ,'50'          ,'spring');
insert into example_students_scores values ('6'    ,'94'          ,'final'       ,'math'        ,'76'          ,'spring');
insert into example_students_scores values ('7'    ,'1023'        ,'quiz'        ,'math'        ,'6'           ,'spring');

我会感激任何指示或提示,只是在上线一周后才弄清楚你的工作是错误的,这是非常尴尬的!

Answer 1

这应该适合你：

select ss2.id score_id,
  ss2.studentid,
  ss1.test,
  ss2.subject,
  ss1.score,
  ss2.semester
from example_students st
left join
(
  select min(score) score, test, subject, studentid
  from example_students_scores
  group by test, studentid, subject
) ss1
  on st.id = ss1.studentid
left join example_students_scores ss2
  on st.id = ss2.studentid
  and ss1.score = ss2.score
  and ss1.test = ss2.test
where st.id = 94
order by ss2.id

请参阅SQL Fiddle 演示