Grouping MySQL data

Question

I have this table, lets call it table one.

+----+---------+-----------------+
| id | link_id | url             |
+----+---------+-----------------+
|  1 |       1 | www.example.com |
|  2 |       1 | www.abc.com     |
|  3 |       1 | www.test.com    |
|  4 |       1 | www.t1.com      |
|  5 |       1 | www.newtest.com |
|  6 |       1 | www.testing.com |
|  7 |       1 | www.abc.com     |
|  8 |       1 | www.example.com |
|  9 |       1 | www.web1.com    |
| 10 |       1 | www.web2.com    |
| 11 |       2 | www.dear.com    |
| 12 |       2 | www.google.com  |
| 13 |       2 | www.flowers.com |
| 14 |       2 | www.yahoo.com   |
| 15 |       2 | www.abc.com     |
| 16 |       2 | www.dell.com    |
| 17 |       2 | www.web.com     |
| 18 |       2 | www.example.com |
| 19 |       2 | www.test.com    |
| 20 |       2 | www.abc.com     |
+----+---------+-----------------+
20 rows in set (0.00 sec)

The link_id is sort the primary identifier in the table. It tells me which urls appear in link 1, link 2 , etc.

What I want to acomplish is: 1. Get all the unique URLs, 2. Show which links the URL belongs to

So an example output would be:

+-----------------+---------+
| url             | link_id |
+-----------------+---------+
| www.example.com |       1 |
| www.example.com |       2 |
| www.abc.com     |       1 |
| www.abc.com     |       2 |
| www.test.com    |       1 |
| www.test.com    |       2 |
| www.t1.com      |       1 |
| www.newtest.com |       1 |
| www.testing.com |       1 |
| www.web1.com    |       1 |

...and so on.

So you can see that www.example.com appears twice since it is associated with both links 1 and 2, but web1.com appears only once since it belongs only to link 1.

I have tried several different group by but I only end up scratching my head even more.

Any help is appreciated. Here is the table dump if anyone needs:

CREATE TABLE IF NOT EXISTS `table1` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `link_id` tinyint(3) unsigned DEFAULT NULL,
  `url` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=21 ;

INSERT INTO `table1` (`id`, `link_id`, `url`) VALUES
(1, 1, 'www.example.com'),
(2, 1, 'www.abc.com'),
(3, 1, 'www.test.com'),
(4, 1, 'www.t1.com'),
(5, 1, 'www.newtest.com'),
(6, 1, 'www.testing.com'),
(7, 1, 'www.abc.com'),
(8, 1, 'www.example.com'),
(9, 1, 'www.web1.com'),
(10, 1, 'www.web2.com'),
(11, 2, 'www.dear.com'),
(12, 2, 'www.google.com'),
(13, 2, 'www.flowers.com'),
(14, 2, 'www.yahoo.com'),
(15, 2, 'www.abc.com'),
(16, 2, 'www.dell.com'),
(17, 2, 'www.web.com'),
(18, 2, 'www.example.com'),
(19, 2, 'www.test.com'),
(20, 2, 'www.abc.com');

Answer 1

Wouldn't a DISTINCT list work? Does order matter?

SELECT DISTINCT url, link_id
FROM `table1`
ORDER BY 1, 2