How do I group columns in MySQL and get rid of recurring ids?

Question

MySQL

+-----+-----+
| id1 | id2 |
+-----+-----+
|  1  |  1  |
+-----+-----+
|  1  |  1  |
+-----+-----+
|  1  |  2  |
+-----+-----+
|  2  |  1  |
+-----+-----+

PHP

$a = mysql_query("SELECT id1, COUNT(id2) AS count FROM table GROUP BY id1");
while($b = mysql_fetch_assoc($a))
{
    echo 'id1: '.$b['id1'].' | count: '.$b['count'].'<br />';
}

Output:

id1: 1 | count: 3
id1: 2 | count: 1

But how do I remove recurring numbers in the column id2 for each id1? For example, the count where id1 is 1 should be 2 instead of 3, because I want to count the 1 in id2 only once, and not twice.

So, the output should actually be:

id1: 1 | count: 2
id1: 2 | count: 1

I hope this makes sense.

Answer 1

SELECT id1, COUNT(DISTINCT id2) ...

Answer 2

SELECT id1, COUNT(DISTINCT id2) AS count FROM table GROUP BY id1

Answer 3

Use a subquery:

SELECT 
  t.id1,COUNT(t.id2) AS count
FROM
  (SELECT DISTINCT id1,id2 FROM table) as t
GROUP BY 
  t.id1