I have two tables:
CREATE TABLE `marks` (
`id_student` int(11) NOT NULL default '0',
`id_subject` int(11) NOT NULL default '0',
`mark` tinyint(4) NOT NULL default '0'
);
CREATE TABLE `subjects` (
`id` int(11) NOT NULL auto_increment,
`name` varchar(50) NOT NULL default '',
PRIMARY KEY (`id`)
);
`marks` table contains the list of marks for all students, the `id_student` field is connected with `id` from `subjects` table. What I need to do is to create a view with marks of specified student, something like:
| subject_id | marks |
| 1 | 1,2,3,4 |
| 2 | 2,2,2,5,4 |
| 3 | 5,5,6 |
...
I know I can handle that with GROUP_CONCAT, but what about earlier versions of MySQL? Can it be done with temp variables and CONCAT_WS function? I tried, but failed. This is not a homework, I just want to know if there is a solution for earlier MySQL versions and that sample seems to be the easiest one to show on.
Thanks.
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yes, it's possible, but you need a temporary table :
CREATE TEMPORARY TABLE t
SELECT
id_subject,
CASE WHEN id_subject = @id_subject THEN @m := CONCAT_WS(',', @m, mark) ELSE @m := mark END AS marks
FROM
marks
WHERE
id_student = 'my student id'
ORDER BY
id_subject;
SELECT
id_subject,
MAX(marks) AS marks
FROM
t
GROUP BY
id_subject
ORDER BY
id_subject;
Thanks for clue. I made my own query based on yours, without temp table. Thanks.
SELECT @m := NULL, @id_subject = 0;
SELECT MAX(CASE WHEN marks.`id_subject` = @id_subject THEN @m := CONCAT_WS(',', @m, marks.`mark`) ELSE @m := marks.`mark` END) AS marks, @id_subject := marks.`id_subject` AS id_subject, subjects.`nazwa` FROM marks, subjects WHERE marks.`id_subject` = subjects.`id` GROUP BY marks.id_subject ORDER BY marks.`id_subject`
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by: akshah123Posted on 2005-09-11 at 08:06:59ID: 14859359
I don't think you can do what you want to do with concat_ws only (at least not in just one query). However, if you are running mysql on windows box. Check out:
http://www.codeproject.com