Say you have a table called "Dogs" that lists all your pets:

Dogs
____________________
ID     DogName   Breed
___________________
1      Fido       ?
2      Prince     ?
3      Fluffy     ?
__________________

...and you would like the field "Breed" for each of the dogs listed to be populated with values that come from a table that contains a list of all the breeds. In the words of the phpMyAdmin manual, you are using a field in one table as a foreign key in another table.

The second table "Breeds" that holds the breed values might look like this:

BREEDS
_____________
ID  Breed
_____________
1    Poodle
2    Terrier
3    Labrador Retriever
4    Beagle
5    Bulldog

If the relation features were enabled, when you edited a record in the Dogs table, you would see a dropdown of the items listed in the Breeds table like this:

This structure eliminates the redundancy of having to enter the same breed over and over in a long list of Dogs, and more importantly you can relate the list of Breeds to any other object in the database, independent of the list of Dogs.

I've found that although hosting services frequently install phpMyAdmin for their users, they rarely enable the table linking features. Users can't configure the hosting services pre-installed phpMyAdmin script to suit themselves, so if you want to use table linking, you will need to set up your own copy of phpMyAdmin within your website directory.

I found it confusing to set up table linking correctly the first time, so here are my simplified setup instructions for phpMyAdmin and enabling table linking.

(Complete documentation for installing phpMyAdmin is in "documentation.html" in the phpMyAdmin directory or HERE.)

DOWNLOAD AND UNPACK THE ARCHIVE

FILL OUT CONFIG.INC.PHP

You will only need to fill out the first list, labeled with a "$i++;" (around line 68).

FILL OUT CONNECTION INFORMATION

Connection information

PMAdb DATABASE INFORMATION

The names of the required tables go in the next few lines. Default suggestions for their names are given in every case. If you change the names of the tables, be sure to change them to match in "scripts/create_tables.sql"

PMAdb section of "config.inc.php"

SAVE AND UPLOAD

Browse to http://yourserver.com/phpMyAdmin/, log in (assuming you password protected phpMyAdmin with one of the authentication schemes), and either create the PMAdb database (if you have the privileges to do so), or decide which existing database to use.

IMPORT THE TABLES INTO PMAdb

A window will appear. Select the database you are going to use from the "Run SQL query/queries on database" dropdown menu. You can enter the data either of two ways:

1) Open the file "scripts/create_tables.sql", copy the contents, and paste them in the query window, then click "Go" or 2) you can import the file by clicking the "Import Files" tab, click the Browse button and browse to the file "scripts/create_tables.sql" then click "Go."

Either method will create the tables and initial data.

When complete, the structure of the PMAdb database should look like this:

RELATION VIEW

Create a new database named DOGSdb, and import the schema for the dogs tables listed at the top of the article into it . Paste the schema shown below into the query window as described above in the " PMAdb.

# SCHEMA FOR DOGSdb---------------------------------------------
#
# Table structure for table `Dogs`
#
# Creation: Sep 27, 2003 at 10:06 PM
# Last update: Sep 27, 2003 at 10:07 PM
#

CREATE TABLE `Dogs` (
  `DogID` tinyint(2) NOT NULL auto_increment,
  `DogName` text,
  `Breed` text,
  PRIMARY KEY  (`DogID`)
) TYPE=MyISAM AUTO_INCREMENT=4 ;

#
# Dumping data for table `Dogs`
#

INSERT INTO `Dogs` VALUES (1, Fido, NULL);
INSERT INTO `Dogs` VALUES (2, 'Prince', NULL);
INSERT INTO `Dogs` VALUES (3, 'Fluffy', NULL); 

# --------------------------------------------------------

#
# Table structure for table `Breeds`
#
# Creation: Sep 27, 2003 at 10:10 PM
# Last update: Sep 27, 2003 at 10:11 PM
#

CREATE TABLE `Breeds` (
  `BreedID` tinyint(25) NOT NULL auto_increment,
  `Breed` text,
  PRIMARY KEY  (`BreedID`)
) TYPE=MyISAM AUTO_INCREMENT=6 ;

#
# Dumping data for table `Breeds`
#

INSERT INTO `Breeds` VALUES (1, 'Poodle');
INSERT INTO `Breeds` VALUES (2, 'Terrier');
INSERT INTO `Breeds` VALUES (3, 'Labrador Retriever');
INSERT INTO `Breeds` VALUES (4, 'Beagle');
INSERT INTO `Breeds` VALUES (5, 'Bulldog'); 

View the table "Dogs" by selecting the database name in the left hand column, then when the list of tables shows up, click on the "Dogs" table name in the list. The [b]Structure[/b] tab will be highlighted and you'll see the structure of the table. Click the [b]Browse[/b] tab. You should see a listing of the three dogs you just imported.

If you click the "EDIT" link next to Fido's name, you should see the edit screen, but the Breeds field will be empty, like this.

Now let's check the Breeds table: In the navigation column on the left, click the "Breeds" link. The structure of the Breeds table should come up: "BreedID" and "Breed "are the two fields that will be listed. If you click the "Browse" tab, you should see a list of all the breeds entered so far.

Click the "Structure" tab again, and then click the words "Relation View" which appear below the horizontal line, and below "Add new field". See the image below -  which shows the link on another table than the ones we are working on.

Click to enlarge.

Breeds Table Relation View 

We need to decide which field will appear as a label when values from the "Breeds" table appear in the "Breed" field of the Dogs table. The actual value that will be related will be the BreedID, but for ease of selecting the correct BreedID, it is easier to use a text label that is associated with that ID.

We only have two fields in this table: BreedID and Breed, and one of them is an ID number, which is not very descriptive. So let's choose the "Breed" field, which has the name of each breed in it.

Do this by selecting Breed from the drop-down menu under "Choose field to display." Click the Go button below that area.

Now we move back to the Dogs table. Click the link to the "Dogs" table in the left hand navigation column. You should be in the "Structure" tab. Click on "Relation View."'

 Dogs table relation view 

 Under "Links to, " select "Breeds->BreedID" from the dropdown menu next to the Breed Field. Only the fields that are indexes ("Breeds->BreedID", "Dogs->DogID") show up here, but our chosen text labels will also display when we edit the Dogs table, since we just set them to do so in the previous screen.

Note that in more recent versions, this task is still under the Structure tab, but instead of clicing the "Choose Field to display" 

Click the "Go" button below the "Links to" area. Now go back and Browse the Dogs table, and try editing any one of the records. You will now see a dropdown menu containing all the breeds in the Breed field!