GROUP_CONCAT With Nested Set Model - php

Question

I have an application that uses a nested set model class to organise my data, however I'm trying to write a query that will group_concat my results. I know I need to put some sub select statements somewhere but I can't figure it out!
Here's my structure at the moment:
table: person
-----------+------------+-----------
|Person_ID | Name | Age |
-----------+------------+-----------
| 1 | Mark Vance | 19 |
| 2 | Michael Tsu| 22 |
| 3 | Mark Jones | 29 |
| 4 | Sara Young | 25 |
-----------+------------+-----------
table: person_to_group
----+------------+-----------
|ID | Person_ID | Group_ID |
----+------------+-----------
| 1 | 3 | 1 |
| 2 | 3 | 2 |
| 3 | 1 | 2 |
| 4 | 4 | 3 |
----+------------+-----------
table: groups
----------+--------------+--------------+-------------
|Group_ID | Group_Name | Group_Left | Group_Right |
----------+--------------+--------------+-------------
| 1 | Root | 1 | 6 |
| 2 | Node | 2 | 5 |
| 3 | Sub Node | 3 | 4 |
----------+--------------+--------------+-------------
I need to render something like this with my results:
//Grab the group_IDs for this person and put them in the class tag...
<li class="2 3">Sara Young is in the Sub Node Group</li>
Notice that although Sara is in the Sub Node group, she is still being given the id for Node aswell because she is a child of Node.
The following is the query that I am working with as a starting point.
SELECT *, GROUP_CONCAT( CAST( gg.Group_ID AS CHAR ) SEPARATOR ' ' ) Group_IDs
FROM groups gg
LEFT JOIN person_to_group AS t1 ON gg.Group_ID = t1.Group_ID
LEFT JOIN person AS t2 ON t2.Person_ID = t1.Person_ID
GROUP BY t2.per_ID
ORDER BY t2.Name ASC
Any help would be much appreciated!

Answer 1

Here's how I'd write the query:
SELECT p.Name,
GROUP_CONCAT( g.Group_Name ) AS Group_List,
GROUP_CONCAT( CAST( gg.Group_ID AS CHAR ) SEPARATOR ' ' ) AS Group_ID_List
FROM person AS p
INNER JOIN person_to_group AS pg ON p.Person_ID = pg.Person_ID
INNER JOIN groups AS g ON pg.Group_ID = g.Group_ID
INNER JOIN groups AS gg ON g.Group_Left BETWEEN gg.Group_Left AND gg.Group_Right
GROUP BY p.Name
ORDER BY p.Name ASC
Note that if you group by person name, you also need to GROUP_CONCAT the list of group names. According to your schema, a person could belong to multiple groups, because of the many-to-many relationship.
I also recommend against using SELECT * in general. Just specify the columns you need.

Answer 2

This was little bit interesting as I do programming in both MsSQL and MySql. In SQL I have used function called STUFF. In MySQL you can use a function called INSERT. I tried out the below query in MsSQL. Don't have a MySQL handy to try out my query. If I have time I will post the MySQL version of the query.
DECLARE #person TABLE (Person_ID INT, Name VARCHAR(50), Age INT)
INSERT INTO #person VALUES
(1,'Mark Vance',19),
(2,'Michael Tsu',22),
(3,'Mark Jones',29),
(4,'Sara Young',25)
DECLARE #groups TABLE (Group_ID INT, Group_Name VARCHAR(50), Group_Left INT, Group_Right INT)
INSERT INTO #groups VALUES
(1,'Root',1,6),
(2,'Node',2,5),
(3,'Sub Node',3,4)
DECLARE #person_to_group TABLE (ID INT, Person_ID INT, Group_ID INT)
INSERT INTO #person_to_group VALUES
(1,3,1),
(2,3,2),
(3,1,1),
(4,4,1),
(4,1,1)
SELECT *,STUFF((SELECT ',' + CAST(g.Group_ID AS VARCHAR) FROM #groups g
JOIN #person_to_group pg ON g.Group_ID = pg.Group_ID AND pg.Person_ID = a.Person_ID FOR XML PATH('')) , 1, 1, '' ) FROM #person a
Function: INSERT(str,pos,len,newstr)
Documentation: http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_insert