Question

What I am trying to do is to access the proper row in a table, so that it returns the right location name, address, etc. The address is returned correctly, but there are three results rather than one. These are our various international locations.

Either my tables aren’t normalized properly or I’m writing my query incorrectly. I can’t figure out which. Maybe a little of both. Here are my tables:

DEALERS TABLE: 

channel_partner_id    company
------------------    --------
626                   Company Inc.
626                   Company GmBH
626                   Company Ltd.

DEALERS_LOCATIONS TABLE:

channel_partner_id    location_id
------------------    -----------
626                   18
626                   19
626                   20

LOCATIONS TABLE:

location_id           address                name_url
----------            --------------------   -------
18                    1234 Anywhere St.      anywhere-st
19                    3245 Nowhere St.       nowhere-st
20                    90 Everywhere St.      everywhere-st

I want to join them on the name_url.

So here’s my query in CodeIgniter/Active Record (which is translated into standard MySQL easy enough):

$this->db->where('l.name_url', $name_url);
$this->db->join('all_dealers_locations dl', 'dl.channel_partner_id = d.channel_partner_id', 'inner');
$this->db->join('all_locations l', 'l.location_id = dl.location_id', 'inner');
$row = $this->db->get('all_dealers d')->row();

But I get back three results from this. Why, if I am using the where clause of the name_url (which is being passed properly into the function)? Is it the type of join I have? I tried left and outer and that didn’t help.

What am I doing wrong?

Answer 1

Your tables have some issues.

The big red flag is that dealers has multiple rows with the same id (which means that channel_partner_id can not be the primary key).

This is a problem because it looks like dealers_locations is supposed to be an intersection table. The standard way to implement such a table is to take the primary keys of the two tables, which in this case would be locations and dealers. Since dealer_locations doesn’t have the primary key of dealers, it’s not going to work.

Here’s how I would implement this instead:

create table dealers (
  channel_partner_id   int primary key,
  name                 varchar(30)
);

create table locations (
  location_id  int primary key,
  address      varchar(30),
  name_url     varchar(30)
);

create table dealer_locations (
  location_id int,
    foreign key (location_id) references locations(location_id),
  channel_partner_id int,
    foreign key (channel_partner_id) references dealers(channel_partner_id),
  primary key (location_id, channel_partner_id)
);

Note the two-part primary key for dealer_locations.