mysql> describe note;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| code  | varchar(30) | NO   |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql> describe tag;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id      | int(11)     | NO   |     | NULL    |       |
| tagname | varchar(25) | NO   |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

mysql> select * from note;
+----+--------+
| id | code   |
+----+--------+
|  1 | Note A |
|  2 | Note A |
|  3 | Note A |
|  4 | Note A |
|  5 | Note A |
|  6 | Note B |
|  7 | Note B |
|  8 | Note B |
|  9 | Note B |
+----+--------+
9 rows in set (0.00 sec)

mysql> select * from tag;
+----+---------+
| id | tagname |
+----+---------+
|  1 | tag1    |
|  2 | tag1    |
|  2 | tag2    |
|  3 | tag3    |
|  4 | tag1    |
|  4 | tag2    |
|  5 | tag3    |
|  6 | tag1    |
|  7 | tag2    |
|  8 | tag1    |
|  8 | tag2    |
|  8 | tag3    |
|  9 | tag1    |
+----+---------+
13 rows in set (0.00 sec)

Details:
Notes have a general grouping code.  Within the group, each note can have a different combination of tags associated.

Goal:  show a summary count of the different combinations of tags for a note, combination only valid for the same note.code.  Ideally it should provide a reference note.id on the summary line so you know what is being counted.  in example:
note.id    count
-------    --------
1          1         <just id=1 has 'tag1'>
2          2         <both id=2 and id=4 have tags 'tag1' and 'tag2'>
3          2         <both id=3 and id=5 have tags 'tag3'>
6          2         <both id=6 and id=9 have tag 'tag1'  NOTE: these are grouped because 1&2 are code 'Note A' and these are code 'Note B'
7          1         <just id=7 has 'tag2'>
8          1         <just id=8 has 'tag1', 'tag2' and 'tag3'>