complex hierarchal SQL query help needed please! - mysql

Question

Calling all mySQL gurus!
I am in need of a complex query for mySQL but I can't get my head around it. There are 2 tables in question:
locations
(columns: location_id, parent, location)
Data is split in a hierarchal fashion into Country, Region, County and Town thus:
1, 0, England (country)
2, 1, South West (region)
3, 1, South East (region)
4, 2, Dorset (county)
5, 4, Bournemouth (town)
6, 4, Poole (town)
7, 4, Wimborne (town)
etc up to 400+ rows of location data
profiles
(columns: profile_id, title, location_id)
Each row has one location ID which is ALWAYS a town (ie the last child of). Eg:
1, 'This profile has location set as Bournemouth', 5
2, 'This profile has location set as Poole', 6
etc
What I need to achieve is to return all IDs from the Locations table where itself or it's children have entries associated with it. So in the example above I would need the following location IDs returned: 1, 2, 4, 5, 6
Reasons:
1 - YES, England is parent of South West, Dorset and Bournemouth which has an entry
2 - YES, South West is parent of Dorset and Bournemouth which has an entry
3 - NO, South East has no entries under it or any of it's children
4 - YES, Dorset is parent of Bournemouth which has an entry
5 - YES, Bournemouth has an entry
6 - YES, Poole has an entry
7 - NO, Wimborne has no entries
So, is this actually possible? I attempted to do it in PHP with nested SQL queries but the script timed out so there must be a way to do this just in a SQL query?
Thanking you in advance! :)
===========
UPDATE
After reading through and playing with all these solutions I realised that I was going about the problem completely the wrong way. Instead of going through all the locations and returning those that have entries it makes more sense and is far more efficient to get all the entries and return the corresponding locations and then go up the hierarchy to get each location parent until the root is hit.
Thank you very much for your help, it at least made me realise that what I was attempting was unnecessary.

Answer 1

The way I have dealt with this is doing only one SQL load, and then putting references inside of the parent objects.
$locations = array();
$obj_query = "SELECT * from locations";
$result_resource = mysql_query($obj_query);
while ($row = mysql_fetch_assoc($result_resource) {
$locations[$row['location_id'] = (object) $row;
}
foreach ($locations as $location) {
if (isset($location->parent) {
$locations[$location->parent]->children[] = $location;
}
}
Your object would then need a method such as this to find out whether a location is a descendant:
function IsAnscestorOF ($location) {
if (empty($children)) { return false; }
if (in_array($location, keys($this->children) {
return true;
} else {
foreach ($children as $child) {
if ($child->isAnscestor) {
return true;
}
}
}
return false;
}

Answer 2

THe fact that your script timed out would indicate an infinite loop somewhere.
Considering you're making a reference to the locations table based on the child area, plus another reference to the parent area, you probalby have to use a combination of PHP & Mysql to scroll through all this - a simple JOIN statement would not work in this case, I don't think.
Also you need to alter the table so that if it's a top-level page, it has a parent_id of NULL, not 0. After you've done that..
$sql = "SELECT * FROM locations WHERE parent =''";
$result = mysql_query($sql);
while($country = mysql_fetch_array($result)) {
$subsql = "SELECT * FROM locations WHERE parent='".$country['id']."'";
$subresult = mysql_query($subsql);
while($subregion = mysql_fetch_array($subresult)) {
$profilesql = "SELECT * FROM profiles WHERE location_id='".$subregion['id']."'";
$profileresult = mysql_query($profilesql);
echo mysql_num_rows($profileresult).' rows under '.$subregion['location'].'.<br />';
}
}
The base code is there... does anybody have a clever idea of making it work with various sub-levels? But honestly, if this were my project, I would have made separate tables for Country, and then Regions, and then City/Town. 3 tables would make the data navigation much easier.

Answer 3

If your php code was good you might have a nested loop in the [location -> parent] fd. I would start there first, and just use PHP. I don't think SQL has a recursive function.
If you NEED a nested parent loop, you should write an mutation of merge|union algorithm to solve this this.
To find the nested loop in PHP
$ids = array();
function nestedLoopFinder($parent)
{
global $ids;
$result = mysql_query("SELECT location_id FROM locations WHERE parent=$parent");
while($row = mysql_fetch_object($result))
{
if(in_array($row->location_id, $ids)) {
die("duplicate found: $row->location_id");
}
$ids[] = $row->location_id;
//recurse
nestedLoopFinder($row->location_id);
}
}

Answer 4

Not sure if I fully understand your requirements but the following stored procedure example might be a good starting point for you:
Example calls (note the included column)
mysql> call location_hier(1);
+-------------+---------------------+--------------------+---------------------+-------+----------+
| location_id | location | parent_location_id | parent_location | depth | included |
+-------------+---------------------+--------------------+---------------------+-------+----------+
| 1 | England (country) | NULL | NULL | 0 | 1 |
| 2 | South West (region) | 1 | England (country) | 1 | 1 |
| 3 | South East (region) | 1 | England (country) | 1 | 0 |
| 4 | Dorset (county) | 2 | South West (region) | 2 | 1 |
| 5 | Bournemouth (town) | 4 | Dorset (county) | 3 | 1 |
| 6 | Poole (town) | 4 | Dorset (county) | 3 | 1 |
| 7 | Wimborne (town) | 4 | Dorset (county) | 3 | 0 |
+-------------+---------------------+--------------------+---------------------+-------+----------+
7 rows in set (0.00 sec)
You'd call the stored procedure from php as follows:
$startLocationID = 1;
$result = $conn->query(sprintf("call location_hier(%d)", $startLocationID));
Full script:
http://pastie.org/1785995
drop table if exists profiles;
create table profiles
(
profile_id smallint unsigned not null auto_increment primary key,
location_id smallint unsigned null,
key (location_id)
)
engine = innodb;
insert into profiles (location_id) values (5),(6);
drop table if exists locations;
create table locations
(
location_id smallint unsigned not null auto_increment primary key,
location varchar(255) not null,
parent_location_id smallint unsigned null,
key (parent_location_id)
)
engine = innodb;
insert into locations (location, parent_location_id) values
('England (country)',null),
('South West (region)',1),
('South East (region)',1),
('Dorset (county)',2),
('Bournemouth (town)',4),
('Poole (town)',4),
('Wimborne (town)',4);
drop procedure if exists location_hier;
delimiter #
create procedure location_hier
(
in p_location_id smallint unsigned
)
begin
declare v_done tinyint unsigned default 0;
declare v_depth smallint unsigned default 0;
create temporary table hier(
parent_location_id smallint unsigned,
location_id smallint unsigned,
depth smallint unsigned default 0,
included tinyint unsigned default 0,
primary key (location_id),
key (parent_location_id)
)engine = memory;
insert into hier select parent_location_id, location_id, v_depth, 0 from locations where location_id = p_location_id;
create temporary table tmp engine=memory select * from hier;
/* http://dev.mysql.com/doc/refman/5.0/en/temporary-table-problems.html */
while not v_done do
if exists( select 1 from locations c
inner join tmp on c.parent_location_id = tmp.location_id and tmp.depth = v_depth) then
insert into hier select c.parent_location_id, c.location_id, v_depth + 1, 0 from locations c
inner join tmp on c.parent_location_id = tmp.location_id and tmp.depth = v_depth;
update hier inner join tmp on hier.location_id = tmp.parent_location_id
set hier.included = 1;
set v_depth = v_depth + 1;
truncate table tmp;
insert into tmp select * from hier where depth = v_depth;
else
set v_done = 1;
end if;
end while;
update hier inner join tmp on hier.location_id = tmp.parent_location_id
set hier.included = 1;
-- include any locations that have profiles ???
update hier inner join profiles on hier.location_id = profiles.location_id
set hier.included = 1;
-- output the results
select
c.location_id,
c.location as location,
p.location_id as parent_location_id,
p.location as parent_location,
hier.depth,
hier.included
from
hier
inner join locations c on hier.location_id = c.location_id
left outer join locations p on hier.parent_location_id = p.location_id
-- where included = 1 -- filter in your php or here up to you !
order by
hier.depth;
-- clean up
drop temporary table if exists hier;
drop temporary table if exists tmp;
end #
delimiter ;
call location_hier(1);
Hope this helps :)