Sammenføj to tabeller (med en 1-M relation), hvor den anden tabel skal "flades ud" til en række

select s.id,s.name,
max(case when e.course_id = 55 then complete else null end) as c55,
max(case when e.course_id = 66 then complete else null end) as c66,
max(case when e.course_id = 77 then complete else null end) as c77
from student as s
left join enrollment as e
on s.id = e.student_id
group by s.id

@Chris. Ved at bruge den lagrede procedure kan du endda oprette dynamisk pivottabel uden at kende antallet af kolonner før. Dette er linket

http://forum.html.it/forum/showthread.php ?s=&threadid=1456236

af et svar fra mig på et italiensk forum på et lignende problem. Der er et komplet eksempel, der kan hjælpe dig til at forstå logikken bag. :)

REDIGER. Opdater med en MYSQL DYNAMISK VISNING

Dette er min startdump:

/*Table structure for table `student` */

drop table if exists `student`;

create table `student` (
  `id` int(10) unsigned not null auto_increment,
  `name` varchar(50) default null,
  primary key (`id`)
) engine=myisam;

/*Data for the table `student` */

insert  into `student`(`id`,`name`) values (1,'chris');
insert  into `student`(`id`,`name`) values (2,'joe');
insert  into `student`(`id`,`name`) values (3,'jack');

drop table if exists enrollment;

create table `enrollment` (
  `enrollment_id` int(11) auto_increment primary key,
  `student_id` int(11) default null,
  `course_id` int(11) default null,
  `complete` varchar(50) default null
) engine=myisam auto_increment=8 default charset=latin1;

/*Data for the table `enrollment` */

insert  into `enrollment`(`enrollment_id`,`student_id`,`course_id`,`complete`) values (1,1,55,'true');
insert  into `enrollment`(`enrollment_id`,`student_id`,`course_id`,`complete`) values (2,1,66,'true');
insert  into `enrollment`(`enrollment_id`,`student_id`,`course_id`,`complete`) values (3,1,77,'true');
insert  into `enrollment`(`enrollment_id`,`student_id`,`course_id`,`complete`) values (4,2,55,'true');
insert  into `enrollment`(`enrollment_id`,`student_id`,`course_id`,`complete`) values (5,2,66,'false');
insert  into `enrollment`(`enrollment_id`,`student_id`,`course_id`,`complete`) values (6,3,55,'false');
insert  into `enrollment`(`enrollment_id`,`student_id`,`course_id`,`complete`) values (7,3,66,'true');

og dette er den lagrede procedure for den dynamiske visning:

delimiter //
drop procedure if exists dynamic_view//
create procedure dynamic_view()
begin
declare finish int default 0;
declare cid int;
declare str varchar(10000) default "select s.id,s.name,";
declare curs cursor for select course_id from enrollment group by course_id;
declare continue handler for not found set finish = 1;
open curs;
my_loop:loop
fetch curs into cid;
if finish = 1 then
leave my_loop;
end if;
set str = concat(str, "max(case when e.course_id = ",cid," then complete else null end) as course_",cid,",");
end loop;
close curs;
set str = substr(str,1,char_length(str)-1);
set @str = concat(str," from student as s
            left join enrollment as e
            on s.id = e.student_id
            group by s.id");
prepare stmt from @str;
execute stmt;
deallocate prepare stmt;
-- select str;
end;//
delimiter ;

Lad os nu kalde det

mysql> call dynamic_view();
+----+-------+-----------+-----------+-----------+
| id | name  | course_55 | course_66 | course_77 |
+----+-------+-----------+-----------+-----------+
|  1 | chris | true      | true      | true      |
|  2 | joe   | true      | false     | NULL      |
|  3 | jack  | false     | true      | NULL      |
+----+-------+-----------+-----------+-----------+
3 rows in set (0.00 sec)

Query OK, 0 rows affected (0.05 sec)

Nu indsætter vi to andre poster med to forskellige kurser:

insert  into `enrollment`(`student_id`,`course_id`,`complete`) values (1,88,'true');
insert  into `enrollment`(`student_id`,`course_id`,`complete`) values (3,99,'true');

og vi husker proceduren. Dette er resultatet:

mysql> call dynamic_view();
+----+-------+-----------+-----------+-----------+-----------+-----------+
| id | name  | course_55 | course_66 | course_77 | course_88 | course_99 |
+----+-------+-----------+-----------+-----------+-----------+-----------+
|  1 | chris | true      | true      | true      | true      | NULL      |
|  2 | joe   | true      | false     | NULL      | NULL      | NULL      |
|  3 | jack  | false     | true      | NULL      | NULL      | true      |
+----+-------+-----------+-----------+-----------+-----------+-----------+
3 rows in set (0.00 sec)

Query OK, 0 rows affected (0.02 sec)

Det er alt. :)