EXPLAIN EXTENDED what is column "filtered" ? (2 replies)

Hi all,

with EXPLAIN EXTENDED (MySQL 5.1.44) I see a new column "filtered".

EXPLAIN EXTENDED 
SELECT kunde_id FROM verkauf
WHERE artikel_id IN ( 10, 30);

+----+-------------+---------+-------+---------------------------+---------------------------+---------+------+------+----------+--------------------------+
| id | select_type | table   | type  | possible_keys             | key                       | key_len | ref  | rows | filtered | Extra                    |
+----+-------------+---------+-------+---------------------------+---------------------------+---------+------+------+----------+--------------------------+
|  1 | SIMPLE      | verkauf | range | idx_verkauf_artikel_kunde | idx_verkauf_artikel_kunde | 4       | NULL |    6 |   100.00 | Using where; Using index |
+----+-------------+---------+-------+---------------------------+---------------------------+---------+------+------+----------+--------------------------+
1 row in set, 1 warning (0.08 sec)

Most of the time, filtered shows "100.00".

What is "100.00" ?
What is "filtered" good for?

with kind regards,
Thomas