MySQL 横向衍生表(Lateral Derived Tables)的实现

create table subject(
id int not null primary key,
sub_name varchar(12),
teacher varchar(12));

insert into subject values (1,'语文','王老师'),(2,'数学','张老师');

create table exam(
id int not null auto_increment primary key,
subject_id int,
student varchar(12),
score int);

insert into exam values(null,1,'小红',87);
insert into exam values(null,1,'小橙',98);
insert into exam values(null,1,'小黄',89);
insert into exam values(null,1,'小绿',98);
insert into exam values(null,2,'小青',77);
insert into exam values(null,2,'小蓝',83);
insert into exam values(null,2,'小紫',99);

select * from subject;
select * from exam;

select s.teacher,e.student,e.score
from subject s
join exam e on e.subject_id=s.id
join (select subject_id, max(score) highest_score from exam group by subject_id) best 
on best.subject_id=e.subject_id and best.highest_score=e.score;

select s.teacher,e.student,e.score
from subject s
join exam e on e.subject_id=s.id
join lateral (select subject_id, max(score) highest_score from exam where exam.subject_id=e.subject_id group by e.subject_id) best 
on best.highest_score=e.score;